Index: /trunk/aclocal.m4
===================================================================
--- /trunk/aclocal.m4	(revision 562)
+++ /trunk/aclocal.m4	(revision 563)
@@ -1244,8 +1244,9 @@
      AC_MSG_CHECKING([whether ${CC} accepts $1])
      saved_cflags="$CFLAGS"
-     CFLAGS="$CFLAGS -Werror $1"
+     # any -Wno- option will always succeed :-(
+     flag_check_opt=`echo $1 | sed 's,-Wno-,-W,'`
+     CFLAGS="$CFLAGS -Werror $flag_check_opt"
      AC_TRY_COMPILE(,, flag_check_cv=yes, flag_check_cv=no)
      CFLAGS="$saved_cflags"
-
      if test $flag_check_cv = yes; then
       	CFLAGS="$CFLAGS $1"