Check for warning flags without no- prefix

config/:
	* warnings.m4 (ACX_PROG_CC_WARNING_OPTS)
	(ACX_PROG_CC_WARNING_ALMOST_PEDANTIC): Run the test without the
	no- prefix.
libdecnumber/:
	* configure: Regenerate.
libiberty/:
	* configure: Regenerate.

libiberty/configure

@@ -3920,8 +3920,14 @@ ac_c_preproc_warn_flag=yes
 
 ac_libiberty_warn_cflags=
 save_CFLAGS="$CFLAGS"
-for option in -W -Wall -Wwrite-strings -Wc++-compat \
+for real_option in -W -Wall -Wwrite-strings -Wc++-compat \
 			  -Wstrict-prototypes; 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-\(.*\)'` ;;
+    *) option=$real_option ;;
+  esac
   as_acx_Woption=`$as_echo "acx_cv_prog_cc_warning_$option" | $as_tr_sh`
 
   { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether $CC supports $option" >&5
@@ -3953,11 +3959,13 @@ eval ac_res=\$$as_acx_Woption
 	       { $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_res" >&5
 $as_echo "$ac_res" >&6; }
   if test `eval 'as_val=${'$as_acx_Woption'};$as_echo "$as_val"'` = yes; then :
-  ac_libiberty_warn_cflags="$ac_libiberty_warn_cflags${ac_libiberty_warn_cflags:+ }$option"
+  ac_libiberty_warn_cflags="$ac_libiberty_warn_cflags${ac_libiberty_warn_cflags:+ }$real_option"
 fi
   done
 CFLAGS="$save_CFLAGS"
 
+# Do the check with the no- prefix removed from the warning options
+# since gcc silently accepts any -Wno-* option on purpose
 if test "$GCC" = yes; then :
   { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether $CC supports -pedantic " >&5
 $as_echo_n "checking whether $CC supports -pedantic ... " >&6; }