Add cmake build to gitlab ci.

Add an additional build job to the gitlab ci pipeline to do a
cmake build. This doesn't run tests, but gives us a little
bit of converage.
2 jobs for gitlab-ci in 2 minutes and 9 seconds
Status Job ID Name Coverage
  Build
passed #10023
docker
autoconf

00:01:40

passed #10024
docker
cmake

00:00:29