[Bug bootstrap/51388] Configure failure to detect unsupported warning options for non-bootstrap builds (including cross builds)

[sch...@linux-m68k.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51388

--- Comment #11 from Andreas Schwab <sch...@linux-m68k.org> 2011-12-20 15:48:28 
UTC ---
Does this work?

diff --git a/config/warnings.m4 b/config/warnings.m4
index 292e5a4..b64b594 100644
--- a/config/warnings.m4
+++ b/config/warnings.m4
@@ -32,7 +32,7 @@ for real_option in $1; do
   # Do the check with the no- prefix removed since gcc silently
   # accepts any -Wno-* option on purpose
   case $real_option in
-    -Wno-*) option=-W`expr $real_option : '-Wno-\(.*\)'` ;;
+    -Wno-*) option=-W`expr x$real_option : 'x-Wno-\(.*\)'` ;;
     *) option=$real_option ;;
   esac
   AS_VAR_PUSHDEF([acx_Woption], [acx_cv_prog_cc_warning_$option])