gitlab-ci: Add ppc64el and s390x cross-build jobs

Using LLVM 8 for ppc64el and 7 for s390x (which hits some coroutine
related issues with LLVM 8).

There are some test failures we need to ignore for now. Also, the
timeout needs to be bumped from the default 30s for some tests, because
they can take longer under emulation.

Reviewed-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3643>
11 files changed