Replace AC_TRY_COMPILE and AC_LANG_

Autoconf 2.50 in 2001 made several macros obsolete. These include macros
for temporary changing the language - AC_LANG_SAVE, AC_LANG_CPLUSPLUS,
AC_LANG_C, and AC_LANG_RESTORE. Instead of these the AC_LANG_PUSH and
AC_LANG_POP macros should be used with later Autoconf versions.

AC_TRY_COMPILE macros should be replaced with AC_COMPILE_IFELSE.

Refs:
- http://git.savannah.gnu.org/cgit/autoconf.git/tree/NEWS
- https://www.gnu.org/software/autoconf/manual/autoconf-2.69/html_node/Language-Choice.html
- https://www.gnu.org/software/autoconf/manual/autoconf-2.69/html_node/Obsolete-Macros.html

1 files changed, 6 insertions, 7 deletions

diff --git a/m4/ax_cxx_have_empty_iostream.m4 b/m4/ax_cxx_have_empty_iostream.m4
index a7d2c7c..54abe79 100644
--- a/m4/ax_cxx_have_empty_iostream.m4
+++ b/m4/ax_cxx_have_empty_iostream.m4
@@ -41,21 +41,20 @@
 #   modified version of the Autoconf Macro, you may extend this special
 #   exception to the GPL to apply to your modified version as well.
 
-#serial 6
+#serial 7
 
 AU_ALIAS([AC_CXX_HAVE_EMPTY_IOSTREAM], [AX_CXX_HAVE_EMPTY_IOSTREAM])
 AC_DEFUN([AX_CXX_HAVE_EMPTY_IOSTREAM],
 [AC_CACHE_CHECK(whether the compiler allow empty iostream,
 ax_cv_cxx_have_empty_iostream,
 [AC_REQUIRE([AX_CXX_NAMESPACES])
-  AC_LANG_SAVE
-  AC_LANG_CPLUSPLUS
-  AC_TRY_COMPILE([#include <iostream>
+  AC_LANG_PUSH([C++])
+  AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <iostream>
 #ifdef HAVE_NAMESPACES
 using namespace std;
-#endif],[iostream iostr; return 0;],
-  ax_cv_cxx_have_empty_iostream=yes, ax_cv_cxx_have_empty_iostream=no)
-  AC_LANG_RESTORE
+#endif]], [[iostream iostr; return 0;]])],
+  [ax_cv_cxx_have_empty_iostream=yes], [ax_cv_cxx_have_empty_iostream=no])
+  AC_LANG_POP([C++])
 ])
 if test "$ax_cv_cxx_have_empty_iostream" = yes; then
    AC_DEFINE(HAVE_EMPTY_IOSTREAM,,[define if the compiler allow empty