Since the 2.16 release of the glibc, 'gets' is not any more defined in the gnulib.
No m4 version synchronized with gnulib since [1] has been released yet.

This patch avoids the following error occurs when building m4 <=1.4.16 on host using
a glibc >=2.16:

make[4]: Entering directory `/opt/buildroot/output/build/host-m4-1.4.16/lib'
/opt/buildroot/output/host/usr/bin/ccache /usr/bin/gcc -std=gnu99  -I.     -O2 -I/opt/buildroot/output/host/include -I/opt/buildroot/output/host/usr/include -MT gl_avltree_oset.o -MD -MP -MF .deps/gl_avltree_oset.Tpo -c -o gl_avltree_oset.o gl_avltree_oset.c
/opt/buildroot/output/host/usr/bin/ccache /usr/bin/gcc -std=gnu99  -I.     -O2 -I/opt/buildroot/output/host/include -I/opt/buildroot/output/host/usr/include -MT c-ctype.o -MD -MP -MF .deps/c-ctype.Tpo -c -o c-ctype.o c-ctype.c
/opt/buildroot/output/host/usr/bin/ccache /usr/bin/gcc -std=gnu99  -I.     -O2 -I/opt/buildroot/output/host/include -I/opt/buildroot/output/host/usr/include -MT c-stack.o -MD -MP -MF .deps/c-stack.Tpo -c -o c-stack.o c-stack.c
/opt/buildroot/output/host/usr/bin/ccache /usr/bin/gcc -std=gnu99  -I.     -O2 -I/opt/buildroot/output/host/include -I/opt/buildroot/output/host/usr/include -MT clean-temp.o -MD -MP -MF .deps/clean-temp.Tpo -c -o clean-temp.o clean-temp.c
mv -f .deps/c-ctype.Tpo .deps/c-ctype.Po
/opt/buildroot/output/host/usr/bin/ccache /usr/bin/gcc -std=gnu99  -I.     -O2 -I/opt/buildroot/output/host/include -I/opt/buildroot/output/host/usr/include -MT close-hook.o -MD -MP -MF .deps/close-hook.Tpo -c -o close-hook.o close-hook.c
In file included from clean-temp.h:22:0,
                 from clean-temp.c:23:
./stdio.h:477:20: error 'gets' undeclared here (not in a function)
make[4]: *** [clean-temp.o] Error 1

References:
[1] http://git.savannah.gnu.org/gitweb/?p=gnulib.git;a=commitdiff;h=66712c23388e93e5c518ebc8515140fa0c807348
[2] http://sources.gentoo.org/cgi-bin/viewvc.cgi/gentoo-x86/sys-devel/m4/files/m4-1.4.16-no-gets.patch?diff_format=h&revision=1.1&view=markup

Signed-off-by: Samuel Martin <s.martin49@gmail.com>

---
diff -purN host-m4-1.4.16.orig/lib/stdio.in.h host-m4-1.4.16/lib/stdio.in.h
--- host-m4-1.4.16.orig/lib/stdio.in.h	2012-07-21 19:11:40.196541826 +0200
+++ host-m4-1.4.16/lib/stdio.in.h	2012-07-21 20:46:05.405850751 +0200
@@ -162,7 +162,9 @@ _GL_WARN_ON_USE (fflush, "fflush is not
    so any use of gets warrants an unconditional warning.  Assume it is
    always declared, since it is required by C89.  */
 #undef gets
+#if defined(__GLIBC__) && !defined(__UCLIBC__) && !__GLIBC_PREREQ(2, 16)
 _GL_WARN_ON_USE (gets, "gets is a security hole - use fgets instead");
+#endif
 
 #if @GNULIB_FOPEN@
 # if @REPLACE_FOPEN@