gitlab CI: add basic build test

Copied from xorgproto

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
2 jobs for master in 2 minutes (queued for 2 seconds)
Status Job ID Name Coverage
  Prep
passed #6775341
container-prep

00:01:27

 
  Build
passed #6775342
autotools

00:00:33