Change guard on <regex.h> inclusion to use new

symbol `! HAVE_LIBC_REGEX' defined in m4/regex.m4.

lib/rpmatch.c

@@ -1,6 +1,6 @@
 /* Determine whether string value is affirmation or negative response
    according to current locale's data.
-   Copyright (C) 1996 Free Software Foundation, Inc.
+   Copyright (C) 1996, 1998 Free Software Foundation, Inc.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -30,10 +30,8 @@
 #endif
 
 #include <sys/types.h>
-#if WITH_REGEX
+#if ! HAVE_LIBC_REGEX
 # include <regex.h>
-#else
-# include <rx.h>
 #endif
 
 #if ENABLE_NLS