Check -W options before using them.

gdb/ChangeLog

@@ -1,3 +1,9 @@
+Thu May 11 21:52:55 2000  Andrew Cagney  <cagney@b1.cygnus.com>
+
+	* configure.in (WERROR_CFLAGS): Check that GCC accepts a -W
+ 	options before using them. Report result.
+	* configure: Regenerate.
+	
 2000-05-11  Elena Zannoni  <ezannoni@kwikemart.cygnus.com>
 
 	* coffread.c (coff_symtab_read): In the case of C_THUMBEXT |

gdb/configure.in

@@ -498,20 +498,27 @@ AC_ARG_ENABLE(build-warnings,
   *)    build_warnings=`echo "${enableval}" | sed -e "s/,/ /g"`;;
 esac
 if test x"$silent" != x"yes" && test x"$build_warnings" != x""; then
-  echo "Setting warning flags = $build_warnings" 6>&1
+  echo "Setting compiler warning flags = $build_warnings" 6>&1
 fi])dnl
 WARN_CFLAGS=""
 WERROR_CFLAGS=""
 if test "x${build_warnings}" != x -a "x$GCC" = xyes
 then
-  # Separate out the -Werror flag as some files just cannot be
-  # compiled with it enabled.
-  for w in ${build_warnings}; do
-    case $w in
-    -Werr*) WERROR_CFLAGS=-Werror ;;
-    *) WARN_CFLAGS="${WARN_CFLAGS} $w"
-    esac
-  done
+    AC_MSG_CHECKING(compiler warning flags)
+    # Separate out the -Werror flag as some files just cannot be
+    # compiled with it enabled.
+    for w in ${build_warnings}; do
+	case $w in
+	-Werr*) WERROR_CFLAGS=-Werror ;;
+	*) # Check that GCC accepts it
+	    if $CC $w 2>&1 | grep 'unrecognized option' > /dev/null; then
+		:
+	    else
+		WARN_CFLAGS="${WARN_CFLAGS} $w"
+	    fi
+	esac
+    done
+    AC_MSG_RESULT(${WARN_CFLAGS}${WERROR_CFLAGS})
 fi
 AC_SUBST(WARN_CFLAGS)
 AC_SUBST(WERROR_CFLAGS)