* configure.in: Document --enable-gcc-warnings better.

ChangeLog

@@ -1,10 +1,13 @@
 2012-07-06  Paul Eggert  <eggert@cs.ucla.edu>
 
+	* configure.in: Document --enable-gcc-warnings better.
+
 	Use c_strcasecmp for ASCII case-insensitive comparison (Bug#11786).
 	This is safer than strcasecmp, which has unspecified behavior
 	outside the POSIX locale and in practice sometimes does not work
 	in multibyte locales.  Similarly for c_strncasecmp and strncasecmp.
 	* configure.in (strcasecmp, strncasecmp): Remove checks.
+
 	* lib/c-ctype.c, lib/c-ctype.h, lib/c-strcase.h, lib/c-strcasecmp.c:
 	* lib/c-strncasecmp.c: New files, taken from gnulib.
 	* lib/gnulib.mk, m4/gnulib-comp.m4: Regenerate.

configure.in

@@ -575,7 +575,9 @@ gl_EARLY
 
 AC_ARG_ENABLE([gcc-warnings],
   [AS_HELP_STRING([--enable-gcc-warnings],
-                  [turn on lots of GCC warnings (for developers)])],
+                  [turn on lots of GCC warnings. This is intended for
+		   developers, and may generate false alarms when used
+		   with older or non-GNU development tools.])],
   [case $enableval in
      yes|no) ;;
      *)      AC_MSG_ERROR([bad value $enableval for gcc-warnings option]) ;;
@@ -597,7 +599,7 @@ if test "${enableval}" != "no"; then
       	 LTO="-flto=$CPUS"
       else
 	 LTO="-flto"
-      fi	 
+      fi
       old_CFLAGS=$CFLAGS
       CFLAGS="$CFLAGS $LTO"
       AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[]], [[]])],