.gitlab-ci.yml: use configure cache file and ccache

This reduces the total time run on CI by caching configure and compilation artifacts.

Checklist

• Code modified for feature

Reviewer's checklist:

• There is a test suite reasonably covering new functionality or modificati
• Function naming, parameters, return values, types, etc., are consistent a
• This feature/change has adequate documentation added
• No obvious mistakes in the code

Relates #292 (closed)