configure: Allow builds with extra warnings

The clang compiler supports a useful compiler option -Weverything,
and GCC also has other warnings not enabled by -Wall.

If glib header files trigger a warning, however, testing glib with
-Werror will always fail. A size mismatch is also detected without
-Werror, so simply remove it.

Cc: qemu-stable@nongnu.org
Signed-off-by: Stefan Weil <sw@weilnetz.de>
Message-Id: <1461879221-13338-1-git-send-email-sw@weilnetz.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

configure

@@ -2985,7 +2985,7 @@ int main(void) {
 }
 EOF
 
-if ! compile_prog "-Werror $CFLAGS" "$LIBS" ; then
+if ! compile_prog "$CFLAGS" "$LIBS" ; then
     error_exit "sizeof(size_t) doesn't match GLIB_SIZEOF_SIZE_T."\
                "You probably need to set PKG_CONFIG_LIBDIR"\
 	       "to point to the right pkg-config files for your"\