Glibc 2.17 doesn't seem to provide it anymore, so do not err on this.

--- ./lib/stdio.in.h.orig	2013-06-21 09:06:17.375268695 +0200
+++ ./lib/stdio.in.h	2013-06-21 09:06:25.418269115 +0200
@@ -151,7 +151,7 @@
    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");
+//_GL_WARN_ON_USE (gets, "gets is a security hole - use fgets instead");
 
 #if @GNULIB_FOPEN@
 # if @REPLACE_FOPEN@