CI: Using multiple stages/jobs

* .gitlab-ci.yml: here.
3 jobs for as/multiple-job-ci in 4 minutes and 25 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Build
passed #34394
check

00:03:07

passed #34395
distcheck

00:04:25

passed #34393
make

00:03:05