ltp: Add support for Imagination Technologies Meta

This patch adds support for Imagination's Meta architecture.
The Meta Linux kernel port will be included in the Linux Kernel
v3.9. The Meta stack grows upwards so we need to add the appropriate
__metag__ macro to the ltp_clone function. Also fix the #if/def
macro for s390x.

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>