Add gitlab ci build description.

Enable a basic build test under gitlab's continuous integration
system so we get some feedback on the state state of each commit
now that we're hosting the upstream repository there.

Signed-off-by: Marvin Scholz <epirat07@gmail.com>
1 job for gitlab-ci in 58 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #10367
docker
autoconf

00:00:58