Fix uClibc build on 64bit platforms by including stdint.h

Fix uClibc build on 64bit platforms by including stdint.h

Fixes an error detected by buildroot autobuilders:
http://autobuild.buildroot.net/results/573/573e2268e205e10d1352fa81122d8f225fdb4575/build-end.log

/home/rclinux/rc-buildroot-test/scripts/instance-1/output/host/mips64el-buildroot-linux-uclibc/sysroot/usr/include/stdint.h:122:27:
error: conflicting types for 'uintptr_t'
 typedef unsigned long int uintptr_t;
                           ^
In file included from ../lib/ldb/tests/ldb_msg.c:17:0:
../third_party/cmocka/cmocka.h:126:28: note: previous declaration of 'uintptr_t' was here
       typedef unsigned int uintptr_t;

The define __WORDSIZE is missing when cmocka.h decides how to
define uintptr_t, this patch includes stdint.h when needed.

Patch sent upstream:
https://lists.samba.org/archive/samba-technical/2018-January/125306.html

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Reviewed-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
Autobuild-User(master): Volker Lendecke <vl@samba.org>
Autobuild-Date(master): Fri Aug 24 17:22:10 CEST 2018 on sn-devel-144