m4: fix errors in shipped stdio.in.h

M4 fails to build against glibc 2.16.x, the shipped stdio.in.h attempts to
wrap gets() with a warning which fails since gets() got removed from the
default _GNU_SOURCE featureset.

SVN-Revision: 32648

tools/m4/patches/100-fix-gets-removal.patch

+--- a/lib/stdio.in.h
++++ b/lib/stdio.in.h
+@@ -158,12 +158,6 @@ _GL_WARN_ON_USE (fflush, "fflush is not 
+                  "use gnulib module fflush for portable POSIX compliance");
+ #endif
+ 
+-/* It is very rare that the developer ever has full control of stdin,
+-   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@
+ #  if !(defined __cplusplus && defined GNULIB_NAMESPACE)