gitlab CI: add a basic build test

Using Arch as base distribution here because we can expect our dependencies to
be up-to-date. We rely on the Arch for our dependencies rather than building
those from git (notably: xorg-macros, xtrans and libxcb).

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
4 jobs for wip/ci-templates in 7 minutes (queued for 1 second)
Status Job ID Name Coverage
  Prep
passed #5640760
check-commits

00:00:21

passed #5640761
container-prep

00:00:12

 
  Build
passed #5640762
build

00:06:17

 
  Deploy
passed #5640763
check-merge-request

00:00:21