Compile controller code in GitLab CI/CD resolving all dependencies

Following this tutorial, it seems that compilation in the GitLab CI/CD subsystem is possible.

The references to external libraries are though not always obvious, therefore more research/clarification is needed.

Current status:

So far, compilation inside a GitLab Docker runner picks up to resolve external libraries, but then fails to find a standard AVR component:

/root/Arduino/libraries/jm_Wire/src/utility/jm_twi.c:25:20: fatal error: avr/io.h: No such file or directory
compilation terminated.