gitlab-ci: introduce stages and dependencies
We're about to add a couple of jobs for Windows. As the Windows runners
are quite slow, we will split those up across two stages: one stage to
build the artifacts, and one stage that runs test slices in parallel.
Introduce stages and "needs" dependencies for the preexisting jobs as a
preparatory step. The stages will lead to a more natural representation
of jobs in the UI, whereas the "needs" dependency ensures that jobs do
not have to wait for all jobs in the preceding stage to finish.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>