[v6] ci: add FreeBSD build
Adding FreeBSD based build to our CI, so bugs can be found earlier.
It also contains a little patch to repair some FTBS regression from a recently merged MR, so the pipeline runs through.
There're still a bunch of warnings, but these will be handled separately.
Changes v6:
- minor syntax cleanups
- resolved conflicts
Changes v5:
- split out xorgproto git url into variable
- tweak PKG_CONFIG_PATH instead of copying over *.pc files
Changes v4:
- added local xorgproto build, since the version on FreeBSD image is too old
Changes v3:
- using date as docker image tag
- added comment on why extra
git gccall is (currently) necessary
Changes v2:
- refactored it
- now using meson-build.sh
- tests still skipped - not working on freebsd yet.
- added patch for cleaning up the FDO_DISTRIBUTION_* variables