Provide way to build using existing C compiler on Windows.

Summary:
There are various distros that build GHC using their own C compilers
such as MSYS2. Currently they have to patch the build scripts everytime.

This patch provides the configure argument `--enable-distro-toolchain`
which allows one to build using any C compiler on the path.

This is also useful for testing new versions of GCC.

Test Plan:
./configure --enable-distro-toolchain && make - && make THREADS=9 test
./validate

Reviewers: austin, hvr, bgamari

Reviewed By: bgamari

Subscribers: rwbarton, thomie, erikd, #ghc_windows_task_force

GHC Trac Issues: #13792

Differential Revision: https://phabricator.haskell.org/D3637

1 files changed, 43 insertions, 4 deletions

diff --git a/configure.ac b/configure.ac
index a32e6b408c..721f0e7b8b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -113,6 +113,17 @@ AC_ARG_ENABLE(tarballs-autodownload,
         TarballsAutodownload=NO
 )
 
+AC_ARG_ENABLE(distro-toolchain,
+[AC_HELP_STRING([--enable-distro-toolchain],
+                [Do not use bundled Windows toolchain binaries.])],
+        EnableDistroToolchain=YES,
+        EnableDistroToolchain=NO
+)
+
+if test "$EnableDistroToolchain" = "YES"; then
+  TarballsAutodownload=NO
+fi
+
 dnl CC_STAGE0 is like the "previous" variable CC (inherited by CC_STAGE[123])
 dnl but instead used by stage0 for bootstrapping stage1
 AC_ARG_VAR(CC_STAGE0, [C compiler command (bootstrap)])
@@ -365,7 +376,7 @@ set_up_tarballs() {
     fi
 }
 
-if test "$HostOS" = "mingw32"
+if test "$HostOS" = "mingw32" -a "$EnableDistroToolchain" = "NO"
 then
     test -d inplace || mkdir inplace
 
@@ -395,6 +406,29 @@ then
     fi
 fi
 
+# We don't want to bundle a MinGW-w64 toolchain
+# So we have to find these individual tools.
+if test "$EnableDistroToolchain" = "YES"
+then
+    # Ideally should use AC_CHECK_TARGET_TOOL but our triples
+    # are screwed up. Configure doesn't think they're ever equal and
+    # so never tried without the prefix.
+    AC_PATH_PROG([CC],[gcc], [clang])
+    AC_PATH_PROG([LD],[ld], [lld])
+    AC_PATH_PROG([NM],[nm])
+    AC_PATH_PROG([AR],[ar])
+    AC_PATH_PROG([RANLIB],[ranlib])
+    AC_PATH_PROG([OBJDUMP],[objdump])
+    AC_PATH_PROG([DllWrap],[dllwrap])
+    AC_PATH_PROG([Windres],[windres])
+
+    DllWrapCmd="$DllWrap"
+    WindresCmd="$Windres"
+
+    AC_SUBST([DllWrapCmd])
+    AC_SUBST([WindresCmd])
+fi
+
 FP_ICONV
 FP_GMP
 FP_CURSES
@@ -461,6 +495,7 @@ fi
 AC_SUBST(CrossCompiling)
 AC_SUBST(CrossCompilePrefix)
 AC_SUBST(TargetPlatformFull)
+AC_SUBST(EnableDistroToolchain)
 
 dnl ** Which gcc to use?
 dnl --------------------------------------------------------------
@@ -621,7 +656,11 @@ SplitObjsBroken=NO
 dnl ** look for `perl'
 case $HostOS_CPP in
 cygwin32|mingw32)
-  PerlCmd=$hardtop/inplace/perl/perl
+  if test "$EnableDistroToolchain" = "NO"; then
+    PerlCmd=$hardtop/inplace/perl/perl
+  else
+    AC_PATH_PROG([PerlCmd],[perl])
+  fi
   ;;
 *)
     AC_PATH_PROG([PerlCmd],[perl])
@@ -1258,8 +1297,8 @@ echo "\
    libtool      : $LibtoolCmd
    objdump      : $ObjdumpCmd
    ranlib       : $RanlibCmd
-   windres      : $Windres
-   dllwrap      : $DllWrap
+   windres      : $WindresCmd
+   dllwrap      : $DllWrapCmd
    Happy        : $HappyCmd ($HappyVersion)
    Alex         : $AlexCmd ($AlexVersion)
    Perl         : $PerlCmd