From c4911f2db36d811896c73c008b4218d8fa9a4730 Mon Sep 17 00:00:00 2001
From: Lasse Collin <lasse.collin@tukaani.org>
Date: Thu, 25 Sep 2014 18:38:48 +0300
Subject: [PATCH] Build: Detect supported compiler warning flags better.

Clang and nowadays also GCC accept any -Wfoobar option
but then may give a warning that an unknown warning option
was specified. To avoid adding unsupported warning options,
the options are now tested with -Werror.

Thanks to Charles Diza.
---
 configure.ac | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/configure.ac b/configure.ac
index 2df67970..e41979bb 100644
--- a/configure.ac
+++ b/configure.ac
@@ -749,8 +749,9 @@ if test "$GCC" = yes ; then
 	do
 		AC_MSG_CHECKING([if $CC accepts $NEW_FLAG])
 		OLD_CFLAGS="$CFLAGS"
-		CFLAGS="$CFLAGS $NEW_FLAG"
-		AC_COMPILE_IFELSE([AC_LANG_SOURCE([void foo(void) { }])], [
+		CFLAGS="$CFLAGS $NEW_FLAG -Werror"
+		AC_COMPILE_IFELSE([AC_LANG_SOURCE(
+				[void foo(void); void foo(void) { }])], [
 			AM_CFLAGS="$AM_CFLAGS $NEW_FLAG"
 			AC_MSG_RESULT([yes])
 		], [