gitlab-ci: Move LLVM/clang 6/7 packages to the x86_build_old image

They're available in Debian 9 (stretch) as well.

This will avoid conflicts with packages from Debian testing.

Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5296>
3 files changed