Assume autoconf >= 2.64.

* gnulib-tool (DEFAULT_AUTOCONF_MINVERSION): Set to 2.64.
* DEPENDENCIES: Require Autoconf 2.64 or newer.
* NEWS: Mention the changed requirement.
* m4/00gnulib.m4 (_m4_divert_diversion, AC_DEFUN_ONCE): Remove macros.
* m4/gnulib-common.m4 (AS_VAR_IF, AS_VAR_COPY): Remove macros.
* m4/absolute-header.m4 (gl_ABSOLUTE_HEADER): Quote pushdef'ed
variables.
* m4/include_next.m4 (gl_NEXT_HEADERS_INTERNAL): Likewise.
* m4/warn-on-use.m4 (gl_WARN_ON_USE_PREPARE): Likewise.
* m4/warnings.m4 (gl_COMPILER_OPTION_IF): Likewise.
(gl_UNKNOWN_WARNINGS_ARE_ERRORS(C), gl_UNKNOWN_WARNINGS_ARE_ERRORS(C++),
gl_UNKNOWN_WARNINGS_ARE_ERRORS(Objective C)): Define through AC_DEFUN.
* m4/manywarnings.m4 (gl_MANYWARN_ALL_GCC(C), gl_MANYWARN_ALL_GCC(C++)):
Likewise.
* m4/iconv.m4 (AM_ICONV): Define through AC_DEFUN_ONCE directly.
* m4/libunistring.m4 (gl_LIBUNISTRING): Likewise.
* m4/configmake.m4: Update comment.

14 files changed, 72 insertions, 121 deletions

diff --git a/ChangeLog b/ChangeLog
index 3325c156e5..f2e8f8472a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,26 @@
 2020-08-16  Bruno Haible  <bruno@clisp.org>
 
+	Assume autoconf >= 2.64.
+	* gnulib-tool (DEFAULT_AUTOCONF_MINVERSION): Set to 2.64.
+	* DEPENDENCIES: Require Autoconf 2.64 or newer.
+	* NEWS: Mention the changed requirement.
+	* m4/00gnulib.m4 (_m4_divert_diversion, AC_DEFUN_ONCE): Remove macros.
+	* m4/gnulib-common.m4 (AS_VAR_IF, AS_VAR_COPY): Remove macros.
+	* m4/absolute-header.m4 (gl_ABSOLUTE_HEADER): Quote pushdef'ed
+	variables.
+	* m4/include_next.m4 (gl_NEXT_HEADERS_INTERNAL): Likewise.
+	* m4/warn-on-use.m4 (gl_WARN_ON_USE_PREPARE): Likewise.
+	* m4/warnings.m4 (gl_COMPILER_OPTION_IF): Likewise.
+	(gl_UNKNOWN_WARNINGS_ARE_ERRORS(C), gl_UNKNOWN_WARNINGS_ARE_ERRORS(C++),
+	gl_UNKNOWN_WARNINGS_ARE_ERRORS(Objective C)): Define through AC_DEFUN.
+	* m4/manywarnings.m4 (gl_MANYWARN_ALL_GCC(C), gl_MANYWARN_ALL_GCC(C++)):
+	Likewise.
+	* m4/iconv.m4 (AM_ICONV): Define through AC_DEFUN_ONCE directly.
+	* m4/libunistring.m4 (gl_LIBUNISTRING): Likewise.
+	* m4/configmake.m4: Update comment.
+
+2020-08-16  Bruno Haible  <bruno@clisp.org>
+
 	sys_ioctl: Simplify.
 	* m4/sys_ioctl_h.m4 (gl_SYS_IOCTL_H): Remove confusing use of
 	AC_INCLUDES_DEFAULT.
diff --git a/DEPENDENCIES b/DEPENDENCIES
index a7ca044eae..e7b959383a 100644
--- a/DEPENDENCIES
+++ b/DEPENDENCIES
@@ -31,7 +31,7 @@ at any time.
   + Download:
     https://ftp.gnu.org/gnu/m4/
 
-* Autoconf 2.63 or newer.
+* Autoconf 2.64 or newer.
   + Mandatory.
   + Homepage:
     https://www.gnu.org/software/autoconf/
diff --git a/NEWS b/NEWS
index 89477472ba..ed88a7ea2b 100644
--- a/NEWS
+++ b/NEWS
@@ -3,6 +3,8 @@ Important general notes
 
 Date        Modules         Changes
 
+2020-08-16  (all)           Automake >= 1.11 and Autoconf >= 2.64 are required.
+
 2019-12-11  Support for     These modules are now supported in C++ mode as well.
             ISO C or POSIX  This means, while the autoconfiguration uses the C
             functions       compiler, the resulting header files and function
diff --git a/gnulib-tool b/gnulib-tool
index 20a2a3e2a7..1ce9c30894 100755
--- a/gnulib-tool
+++ b/gnulib-tool
@@ -48,11 +48,11 @@ nl='
 '
 IFS=" ""	$nl"
 
-# You can set AUTOCONFPATH to empty if autoconf 2.63 is already in your PATH.
+# You can set AUTOCONFPATH to empty if autoconf 2.64 is already in your PATH.
 AUTOCONFPATH=
 #case $USER in
 #  bruno )
-#    AUTOCONFBINDIR=/arch/x86-linux/gnu-inst-autoconf/2.63/bin
+#    AUTOCONFBINDIR=/arch/x86-linux/gnu-inst-autoconf/2.64/bin
 #    AUTOCONFPATH="eval env PATH=${AUTOCONFBINDIR}:\$PATH "
 #    ;;
 #esac
@@ -1541,7 +1541,7 @@ func_determine_path_separator
 
   # Determine the minimum supported autoconf version from the project's
   # configure.ac.
-  DEFAULT_AUTOCONF_MINVERSION="2.63"
+  DEFAULT_AUTOCONF_MINVERSION="2.64"
   autoconf_minversion=
   configure_ac=
   if case "$mode" in import | add-import | remove-import | update) true;; *) false;; esac \
@@ -1588,8 +1588,8 @@ func_determine_path_separator
     autoconf_minversion=$DEFAULT_AUTOCONF_MINVERSION
   fi
   case "$autoconf_minversion" in
-    1.* | 2.[0-5]* | 2.6[0-2]*)
-      func_fatal_error "minimum supported autoconf version is 2.63. Try adding AC_PREREQ([$DEFAULT_AUTOCONF_MINVERSION]) to your configure.ac." ;;
+    1.* | 2.[0-5]* | 2.6[0-3]*)
+      func_fatal_error "minimum supported autoconf version is 2.64. Try adding AC_PREREQ([$DEFAULT_AUTOCONF_MINVERSION]) to your configure.ac." ;;
   esac
 
   # Remove trailing slashes from the directory names. This is necessary for
diff --git a/m4/00gnulib.m4 b/m4/00gnulib.m4
index 06eff4f386..14628c363b 100644
--- a/m4/00gnulib.m4
+++ b/m4/00gnulib.m4
@@ -1,44 +1,12 @@
-# 00gnulib.m4 serial 7
+# 00gnulib.m4 serial 8
 dnl Copyright (C) 2009-2020 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
 dnl with or without modifications, as long as this notice is preserved.
 
 dnl This file must be named something that sorts before all other
-dnl gnulib-provided .m4 files.  The first part is needed until such time
-dnl as we can assume Autoconf 2.64, with its improved AC_DEFUN_ONCE and
-dnl m4_divert semantics.  The second part is needed until the clang fix
-dnl has been included in Autoconf.
-
-# Until autoconf 2.63, handling of the diversion stack required m4_init
-# to be called first; but this does not happen with aclocal.  Wrapping
-# the entire execution in another layer of the diversion stack fixes this.
-# Worse, prior to autoconf 2.62, m4_wrap depended on the underlying m4
-# for whether it was FIFO or LIFO; in order to properly balance with
-# m4_init, we need to undo our push just before anything wrapped within
-# the m4_init body.  The way to ensure this is to wrap both sides of
-# m4_init with a one-shot macro that does the pop at the right time.
-m4_ifndef([_m4_divert_diversion],
-[m4_divert_push([KILL])
-m4_define([gl_divert_fixup], [m4_divert_pop()m4_define([$0])])
-m4_define([m4_init],
-  [gl_divert_fixup()]m4_defn([m4_init])[gl_divert_fixup()])])
-
-
-# AC_DEFUN_ONCE([NAME], VALUE)
-# ----------------------------
-# Define NAME to expand to VALUE on the first use (whether by direct
-# expansion, or by AC_REQUIRE), and to nothing on all subsequent uses.
-# Avoid bugs in AC_REQUIRE in Autoconf 2.63 and earlier.  This
-# definition is slower than the version in Autoconf 2.64, because it
-# can only use interfaces that existed since 2.59; but it achieves the
-# same effect.  Quoting is necessary to avoid confusing Automake.
-m4_version_prereq([2.63.263], [],
-[m4_define([AC][_DEFUN_ONCE],
-  [AC][_DEFUN([$1],
-    [AC_REQUIRE([_gl_DEFUN_ONCE([$1])],
-      [m4_indir([_gl_DEFUN_ONCE([$1])])])])]dnl
-[AC][_DEFUN([_gl_DEFUN_ONCE([$1])], [$2])])])
+dnl gnulib-provided .m4 files.  It is needed until the clang fix has
+dnl been included in Autoconf.
 
 # The following definitions arrange to use a compiler option
 # -Werror=implicit-function-declaration in AC_CHECK_DECL, when the
diff --git a/m4/absolute-header.m4 b/m4/absolute-header.m4
index 39726ba57b..c043233de3 100644
--- a/m4/absolute-header.m4
+++ b/m4/absolute-header.m4
@@ -1,4 +1,4 @@
-# absolute-header.m4 serial 16
+# absolute-header.m4 serial 17
 dnl Copyright (C) 2006-2020 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -22,23 +22,21 @@ dnl From Derek Price.
 AC_DEFUN([gl_ABSOLUTE_HEADER],
 [AC_REQUIRE([AC_CANONICAL_HOST])
 AC_LANG_PREPROC_REQUIRE()dnl
-dnl FIXME: gl_absolute_header and ac_header_exists must be used unquoted
-dnl until we can assume autoconf 2.64 or newer.
 m4_foreach_w([gl_HEADER_NAME], [$1],
   [AS_VAR_PUSHDEF([gl_absolute_header],
                   [gl_cv_absolute_]m4_defn([gl_HEADER_NAME]))dnl
   AC_CACHE_CHECK([absolute name of <]m4_defn([gl_HEADER_NAME])[>],
-    m4_defn([gl_absolute_header]),
+    [gl_absolute_header],
     [AS_VAR_PUSHDEF([ac_header_exists],
                     [ac_cv_header_]m4_defn([gl_HEADER_NAME]))dnl
     AC_CHECK_HEADERS_ONCE(m4_defn([gl_HEADER_NAME]))dnl
-    if test AS_VAR_GET(ac_header_exists) = yes; then
+    if test AS_VAR_GET([ac_header_exists]) = yes; then
       gl_ABSOLUTE_HEADER_ONE(m4_defn([gl_HEADER_NAME]))
     fi
     AS_VAR_POPDEF([ac_header_exists])dnl
     ])dnl
   AC_DEFINE_UNQUOTED(AS_TR_CPP([ABSOLUTE_]m4_defn([gl_HEADER_NAME])),
-                     ["AS_VAR_GET(gl_absolute_header)"],
+                     ["AS_VAR_GET([gl_absolute_header])"],
                      [Define this to an absolute name of <]m4_defn([gl_HEADER_NAME])[>.])
   AS_VAR_POPDEF([gl_absolute_header])dnl
 ])dnl
diff --git a/m4/configmake.m4 b/m4/configmake.m4
index 0ca6416ac1..f0f094f5f5 100644
--- a/m4/configmake.m4
+++ b/m4/configmake.m4
@@ -1,4 +1,4 @@
-# configmake.m4 serial 3
+# configmake.m4 serial 4
 dnl Copyright (C) 2010-2020 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -9,7 +9,7 @@ AC_PREREQ([2.60])
 # gl_CONFIGMAKE_PREP
 # ------------------
 # Guarantee all of the standard directory variables, even when used with
-# autoconf 2.63 (runstatedir wasn't supported before 2.70) or
+# autoconf 2.64 (runstatedir wasn't supported before 2.70) or
 # automake 1.11 (runstatedir isn't supported even in 1.16.1).
 AC_DEFUN([gl_CONFIGMAKE_PREP],
 [
diff --git a/m4/gnulib-common.m4 b/m4/gnulib-common.m4
index c7d1e34f6a..33e56faa98 100644
--- a/m4/gnulib-common.m4
+++ b/m4/gnulib-common.m4
@@ -1,4 +1,4 @@
-# gnulib-common.m4 serial 56
+# gnulib-common.m4 serial 57
 dnl Copyright (C) 2007-2020 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -480,14 +480,6 @@ AC_DEFUN([gl_FEATURES_H],
   AC_SUBST([HAVE_FEATURES_H])
 ])
 
-# AS_VAR_IF(VAR, VALUE, [IF-MATCH], [IF-NOT-MATCH])
-# ----------------------------------------------------
-# Backport of autoconf-2.63b's macro.
-# Remove this macro when we can assume autoconf >= 2.64.
-m4_ifndef([AS_VAR_IF],
-[m4_define([AS_VAR_IF],
-[AS_IF([test x"AS_VAR_GET([$1])" = x""$2], [$3], [$4])])])
-
 # gl_PROG_CC_C99
 # Modifies the value of the shell variable CC in an attempt to make $CC
 # understand ISO C99 source code.
@@ -660,10 +652,6 @@ AC_DEFUN([gl_CACHE_VAL_SILENT],
   as_echo_n="$saved_as_echo_n"
 ])
 
-# AS_VAR_COPY was added in autoconf 2.63b
-m4_define_default([AS_VAR_COPY],
-[AS_LITERAL_IF([$1[]$2], [$1=$$2], [eval $1=\$$2])])
-
 dnl Expands to some code for use in .c programs that, on native Windows, defines
 dnl the Microsoft deprecated alias function names to the underscore-prefixed
 dnl actual function names. With this macro, these function names are available
diff --git a/m4/iconv.m4 b/m4/iconv.m4
index e593b7270a..67dbfed64f 100644
--- a/m4/iconv.m4
+++ b/m4/iconv.m4
@@ -1,4 +1,4 @@
-# iconv.m4 serial 21
+# iconv.m4 serial 22
 dnl Copyright (C) 2000-2002, 2007-2014, 2016-2020 Free Software Foundation,
 dnl Inc.
 dnl This file is free software; the Free Software Foundation
@@ -7,6 +7,8 @@ dnl with or without modifications, as long as this notice is preserved.
 
 dnl From Bruno Haible.
 
+AC_PREREQ([2.64])
+
 AC_DEFUN([AM_ICONV_LINKFLAGS_BODY],
 [
   dnl Prerequisites of AC_LIB_LINKFLAGS_BODY.
@@ -225,8 +227,7 @@ AC_DEFUN([AM_ICONV_LINK],
   AC_SUBST([LTLIBICONV])
 ])
 
-dnl Define AM_ICONV using AC_DEFUN_ONCE for Autoconf >= 2.64, in order to
-dnl avoid warnings like
+dnl Define AM_ICONV using AC_DEFUN_ONCE, in order to avoid warnings like
 dnl "warning: AC_REQUIRE: `AM_ICONV' was expanded before it was required".
 dnl This is tricky because of the way 'aclocal' is implemented:
 dnl - It requires defining an auxiliary macro whose name ends in AC_DEFUN.
@@ -234,16 +235,7 @@ dnl   Otherwise aclocal's initial scan pass would miss the macro definition.
 dnl - It requires a line break inside the AC_DEFUN_ONCE and AC_DEFUN expansions.
 dnl   Otherwise aclocal would emit many "Use of uninitialized value $1"
 dnl   warnings.
-m4_define([gl_iconv_AC_DEFUN],
-  m4_version_prereq([2.64],
-    [[AC_DEFUN_ONCE(
-        [$1], [$2])]],
-    [m4_ifdef([gl_00GNULIB],
-       [[AC_DEFUN_ONCE(
-           [$1], [$2])]],
-       [[AC_DEFUN(
-           [$1], [$2])]])]))
-gl_iconv_AC_DEFUN([AM_ICONV],
+AC_DEFUN_ONCE([AM_ICONV],
 [
   AM_ICONV_LINK
   if test "$am_cv_func_iconv" = yes; then
diff --git a/m4/include_next.m4 b/m4/include_next.m4
index 9009e293b5..33601aa3b4 100644
--- a/m4/include_next.m4
+++ b/m4/include_next.m4
@@ -1,4 +1,4 @@
-# include_next.m4 serial 24
+# include_next.m4 serial 25
 dnl Copyright (C) 2006-2020 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -176,42 +176,40 @@ AC_DEFUN([gl_NEXT_HEADERS_INTERNAL],
     [AC_CHECK_HEADERS_ONCE([$1])
     ])
 
-dnl FIXME: gl_next_header and gl_header_exists must be used unquoted
-dnl until we can assume autoconf 2.64 or newer.
   m4_foreach_w([gl_HEADER_NAME], [$1],
     [AS_VAR_PUSHDEF([gl_next_header],
                     [gl_cv_next_]m4_defn([gl_HEADER_NAME]))
      if test $gl_cv_have_include_next = yes; then
-       AS_VAR_SET(gl_next_header, ['<'gl_HEADER_NAME'>'])
+       AS_VAR_SET([gl_next_header], ['<'gl_HEADER_NAME'>'])
      else
        AC_CACHE_CHECK(
          [absolute name of <]m4_defn([gl_HEADER_NAME])[>],
-         m4_defn([gl_next_header]),
+         [gl_next_header],
          [m4_if([$2], [check],
             [AS_VAR_PUSHDEF([gl_header_exists],
                             [ac_cv_header_]m4_defn([gl_HEADER_NAME]))
-             if test AS_VAR_GET(gl_header_exists) = yes; then
+             if test AS_VAR_GET([gl_header_exists]) = yes; then
              AS_VAR_POPDEF([gl_header_exists])
             ])
            gl_ABSOLUTE_HEADER_ONE(gl_HEADER_NAME)
            AS_VAR_COPY([gl_header], [gl_cv_absolute_]AS_TR_SH(gl_HEADER_NAME))
-           AS_VAR_SET(gl_next_header, ['"'$gl_header'"'])
+           AS_VAR_SET([gl_next_header], ['"'$gl_header'"'])
           m4_if([$2], [check],
             [else
-               AS_VAR_SET(gl_next_header, ['<'gl_HEADER_NAME'>'])
+               AS_VAR_SET([gl_next_header], ['<'gl_HEADER_NAME'>'])
              fi
             ])
          ])
      fi
      AC_SUBST(
        AS_TR_CPP([NEXT_]m4_defn([gl_HEADER_NAME])),
-       [AS_VAR_GET(gl_next_header)])
+       [AS_VAR_GET([gl_next_header])])
      if test $gl_cv_have_include_next = yes || test $gl_cv_have_include_next = buggy; then
        # INCLUDE_NEXT_AS_FIRST_DIRECTIVE='include_next'
        gl_next_as_first_directive='<'gl_HEADER_NAME'>'
      else
        # INCLUDE_NEXT_AS_FIRST_DIRECTIVE='include'
-       gl_next_as_first_directive=AS_VAR_GET(gl_next_header)
+       gl_next_as_first_directive=AS_VAR_GET([gl_next_header])
      fi
      AC_SUBST(
        AS_TR_CPP([NEXT_AS_FIRST_DIRECTIVE_]m4_defn([gl_HEADER_NAME])),
diff --git a/m4/libunistring.m4 b/m4/libunistring.m4
index 8b6ef8db8d..a0c36e37d2 100644
--- a/m4/libunistring.m4
+++ b/m4/libunistring.m4
@@ -1,9 +1,11 @@
-# libunistring.m4 serial 11
+# libunistring.m4 serial 12
 dnl Copyright (C) 2009-2020 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
 dnl with or without modifications, as long as this notice is preserved.
 
+AC_PREREQ([2.64])
+
 dnl gl_LIBUNISTRING
 dnl Searches for an installed libunistring.
 dnl If found, it sets and AC_SUBSTs HAVE_LIBUNISTRING=yes and the LIBUNISTRING
@@ -12,8 +14,8 @@ dnl augments the CPPFLAGS variable, and #defines HAVE_LIBUNISTRING to 1.
 dnl Otherwise, it sets and AC_SUBSTs HAVE_LIBUNISTRING=no and LIBUNISTRING and
 dnl LTLIBUNISTRING to empty.
 
-dnl Define gl_LIBUNISTRING using AC_DEFUN_ONCE for Autoconf >= 2.64, in order
-dnl to avoid warnings like
+dnl Define gl_LIBUNISTRING using AC_DEFUN_ONCE, in order dnl to avoid warnings
+dnl like
 dnl "warning: AC_REQUIRE: `gl_LIBUNISTRING' was expanded before it was required".
 dnl This is tricky because of the way 'aclocal' is implemented:
 dnl - It requires defining an auxiliary macro whose name ends in AC_DEFUN.
@@ -21,16 +23,7 @@ dnl   Otherwise aclocal's initial scan pass would miss the macro definition.
 dnl - It requires a line break inside the AC_DEFUN_ONCE and AC_DEFUN expansions.
 dnl   Otherwise aclocal would emit many "Use of uninitialized value $1"
 dnl   warnings.
-m4_define([gl_libunistring_AC_DEFUN],
-  m4_version_prereq([2.64],
-    [[AC_DEFUN_ONCE(
-        [$1], [$2])]],
-    [m4_ifdef([gl_00GNULIB],
-       [[AC_DEFUN_ONCE(
-           [$1], [$2])]],
-       [[AC_DEFUN(
-           [$1], [$2])]])]))
-gl_libunistring_AC_DEFUN([gl_LIBUNISTRING],
+AC_DEFUN_ONCE([gl_LIBUNISTRING],
 [
   AC_BEFORE([$0], [gl_LIBUNISTRING_MODULE])
   AC_BEFORE([$0], [gl_LIBUNISTRING_LIBHEADER])
diff --git a/m4/manywarnings.m4 b/m4/manywarnings.m4
index d18da048d9..a37cd15b69 100644
--- a/m4/manywarnings.m4
+++ b/m4/manywarnings.m4
@@ -1,4 +1,4 @@
-# manywarnings.m4 serial 20
+# manywarnings.m4 serial 21
 dnl Copyright (C) 2008-2020 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -39,8 +39,7 @@ AC_DEFUN([gl_MANYWARN_ALL_GCC],
 [_AC_LANG_DISPATCH([$0], _AC_LANG, $@)])
 
 # Specialization for _AC_LANG = C.
-# Use of m4_defun rather than AC_DEFUN works around a bug in autoconf < 2.63b.
-m4_defun([gl_MANYWARN_ALL_GCC(C)],
+AC_DEFUN([gl_MANYWARN_ALL_GCC(C)],
 [
   AC_LANG_PUSH([C])
 
@@ -210,8 +209,7 @@ m4_defun([gl_MANYWARN_ALL_GCC(C)],
 ])
 
 # Specialization for _AC_LANG = C++.
-# Use of m4_defun rather than AC_DEFUN works around a bug in autoconf < 2.63b.
-m4_defun([gl_MANYWARN_ALL_GCC(C++)],
+AC_DEFUN([gl_MANYWARN_ALL_GCC(C++)],
 [
   gl_MANYWARN_ALL_GCC_CXX_IMPL([$1])
 ])
diff --git a/m4/warn-on-use.m4 b/m4/warn-on-use.m4
index 5c8ee45092..f36551c110 100644
--- a/m4/warn-on-use.m4
+++ b/m4/warn-on-use.m4
@@ -1,4 +1,4 @@
-# warn-on-use.m4 serial 6
+# warn-on-use.m4 serial 7
 dnl Copyright (C) 2010-2020 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -30,17 +30,15 @@ AC_DEFUN([gl_WARN_ON_USE_PREPARE],
        [AH_TEMPLATE([HAVE_RAW_DECL_]AS_TR_CPP(m4_defn([gl_decl])),
          [Define to 1 if ]m4_defn([gl_decl])[ is declared even after
           undefining macros.])])dnl
-dnl FIXME: gl_Symbol must be used unquoted until we can assume
-dnl autoconf 2.64 or newer.
      for gl_func in m4_flatten([$2]); do
        AS_VAR_PUSHDEF([gl_Symbol], [gl_cv_have_raw_decl_$gl_func])dnl
        AC_CACHE_CHECK([whether $gl_func is declared without a macro],
-         gl_Symbol,
+         [gl_Symbol],
          [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([$1],
 [@%:@undef $gl_func
   (void) $gl_func;])],
-           [AS_VAR_SET(gl_Symbol, [yes])], [AS_VAR_SET(gl_Symbol, [no])])])
-       AS_VAR_IF(gl_Symbol, [yes],
+           [AS_VAR_SET([gl_Symbol], [yes])], [AS_VAR_SET([gl_Symbol], [no])])])
+       AS_VAR_IF([gl_Symbol], [yes],
          [AC_DEFINE_UNQUOTED(AS_TR_CPP([HAVE_RAW_DECL_$gl_func]), [1])
           dnl shortcut - if the raw declaration exists, then set a cache
           dnl variable to allow skipping any later AC_CHECK_DECL efforts
diff --git a/m4/warnings.m4 b/m4/warnings.m4
index d272365f0a..e01dc6c8ee 100644
--- a/m4/warnings.m4
+++ b/m4/warnings.m4
@@ -1,4 +1,4 @@
-# warnings.m4 serial 14
+# warnings.m4 serial 15
 dnl Copyright (C) 2008-2020 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -23,8 +23,6 @@ m4_ifdef([AS_VAR_APPEND],
 # The effects of this macro depend on the current language (_AC_LANG).
 AC_DEFUN([gl_COMPILER_OPTION_IF],
 [
-dnl FIXME: gl_Warn must be used unquoted until we can assume Autoconf
-dnl 2.64 or newer.
 AS_VAR_PUSHDEF([gl_Warn], [gl_cv_warn_[]_AC_LANG_ABBREV[]_$1])dnl
 AS_VAR_PUSHDEF([gl_Flags], [_AC_LANG_PREFIX[]FLAGS])dnl
 AS_LITERAL_IF([$1],
@@ -34,13 +32,13 @@ case $gl_positive in
   -Wno-*) gl_positive=-W`expr "X$gl_positive" : 'X-Wno-\(.*\)'` ;;
 esac
 m4_pushdef([gl_Positive], [$gl_positive])])dnl
-AC_CACHE_CHECK([whether _AC_LANG compiler handles $1], m4_defn([gl_Warn]), [
+AC_CACHE_CHECK([whether _AC_LANG compiler handles $1], [gl_Warn], [
   gl_save_compiler_FLAGS="$gl_Flags"
   gl_AS_VAR_APPEND(m4_defn([gl_Flags]),
     [" $gl_unknown_warnings_are_errors ]m4_defn([gl_Positive])["])
   AC_LINK_IFELSE([m4_default([$4], [AC_LANG_PROGRAM([])])],
-                 [AS_VAR_SET(gl_Warn, [yes])],
-                 [AS_VAR_SET(gl_Warn, [no])])
+                 [AS_VAR_SET([gl_Warn], [yes])],
+                 [AS_VAR_SET([gl_Warn], [no])])
   gl_Flags="$gl_save_compiler_FLAGS"
 ])
 AS_VAR_IF(gl_Warn, [yes], [$2], [$3])
@@ -59,8 +57,7 @@ AC_DEFUN([gl_UNKNOWN_WARNINGS_ARE_ERRORS],
 [_AC_LANG_DISPATCH([$0], _AC_LANG, $@)])
 
 # Specialization for _AC_LANG = C. This macro can be AC_REQUIREd.
-# Use of m4_defun rather than AC_DEFUN works around a bug in autoconf < 2.63b.
-m4_defun([gl_UNKNOWN_WARNINGS_ARE_ERRORS(C)],
+AC_DEFUN([gl_UNKNOWN_WARNINGS_ARE_ERRORS(C)],
 [
   AC_LANG_PUSH([C])
   gl_UNKNOWN_WARNINGS_ARE_ERRORS_IMPL
@@ -68,8 +65,7 @@ m4_defun([gl_UNKNOWN_WARNINGS_ARE_ERRORS(C)],
 ])
 
 # Specialization for _AC_LANG = C++. This macro can be AC_REQUIREd.
-# Use of m4_defun rather than AC_DEFUN works around a bug in autoconf < 2.63b.
-m4_defun([gl_UNKNOWN_WARNINGS_ARE_ERRORS(C++)],
+AC_DEFUN([gl_UNKNOWN_WARNINGS_ARE_ERRORS(C++)],
 [
   AC_LANG_PUSH([C++])
   gl_UNKNOWN_WARNINGS_ARE_ERRORS_IMPL
@@ -77,8 +73,7 @@ m4_defun([gl_UNKNOWN_WARNINGS_ARE_ERRORS(C++)],
 ])
 
 # Specialization for _AC_LANG = Objective C. This macro can be AC_REQUIREd.
-# Use of m4_defun rather than AC_DEFUN works around a bug in autoconf < 2.63b.
-m4_defun([gl_UNKNOWN_WARNINGS_ARE_ERRORS(Objective C)],
+AC_DEFUN([gl_UNKNOWN_WARNINGS_ARE_ERRORS(Objective C)],
 [
   AC_LANG_PUSH([Objective C])
   gl_UNKNOWN_WARNINGS_ARE_ERRORS_IMPL