[gimp] m4macros: make detectcflags.m4 more reliable

[Michael Natterer <mitch src gnome org>]

commit 990c91f2a7b3eece87477e3dd9af8463993c7c03
Author: Michael Natterer <mitch gimp org>
Date:   Sun Nov 8 01:04:16 2015 +0100

    m4macros: make detectcflags.m4 more reliable
    
    GIMP_DETECT_CFLAGS: pass -Werror to the compiler when checking for
    flags, so the macro fails if passing a flag only warns but doesn't
    cause the compiler to fail. Before, the compiler would warn about the
    flag for each file compiled.

 m4macros/detectcflags.m4 |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/m4macros/detectcflags.m4 b/m4macros/detectcflags.m4
index ad8a099..ee33456 100644
--- a/m4macros/detectcflags.m4
+++ b/m4macros/detectcflags.m4
@@ -7,7 +7,7 @@ AC_DEFUN([GIMP_DETECT_CFLAGS],
   for flag in $2; do
     if test -z "[$]$1"; then
       $1_save_CFLAGS="$CFLAGS"
-      CFLAGS="$CFLAGS $flag"
+      CFLAGS="$CFLAGS -Werror $flag"
       AC_MSG_CHECKING([whether [$]CC understands [$]flag])
       AC_TRY_COMPILE([], [], [$1_works=yes], [$1_works=no])
       AC_MSG_RESULT([$]$1_works)