Add gitlab CI

A very simple CI for now, just make sure it builds.

Largely inspired by the implementation in libinput by Peter Hutterer
<peter.hutterer@who-t.net>.

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
5 jobs for gitlab-ci in 42 seconds (queued for 10 seconds)
Status Name Job ID Coverage
  Sanity Check
passed check-ci-script #12250147

00:00:07

passed check-commit #12250148

00:00:09

passed check-merge-request #12250149

00:00:08

 
  Prep
passed prep-fedora-34 #12250150

00:00:15

 
  Build
passed build-fedora-34 #12250151

00:00:17