http://sources.gentoo.org/cgi-bin/viewvc.cgi/gentoo-x86/sys-devel/m4/files/m4-1.4.16-no-gets.patch?revision=1.1

https://bugs.gentoo.org/424978

hack until m4 pulls a newer gnulib version

From 66712c23388e93e5c518ebc8515140fa0c807348 Mon Sep 17 00:00:00 2001
From: Eric Blake <eblake@redhat.com>
Date: Thu, 29 Mar 2012 13:30:41 -0600
Subject: [PATCH] stdio: don't assume gets any more

Gnulib intentionally does not have a gets module, and now that C11
and glibc have dropped it, we should be more proactive about warning
any user on a platform that still has a declaration of this dangerous
interface.

--- a/lib/stdio.in.h
+++ b/lib/stdio.in.h
@@ -125,7 +125,6 @@
    so any use of gets warrants an unconditional warning.  Assume it is
    always declared, since it is required by C89.  */
 #undef gets
-_GL_WARN_ON_USE (gets, "gets is a security hole - use fgets instead");
 
 #if @GNULIB_FOPEN@
 # if @REPLACE_FOPEN@