Add CI for FreeBSD

[AkihiroSuda]

We should run the unit test on FreeBSD, probably using Vagrant on macOS instances of GHA.

[koobs]

@AkihiroSuda Is Cirrus CI an option? Failing that I'm happy to setup a FreeBSD buildbot worker for you (I run one for several upstreams including Python)

[AkihiroSuda]

SGTM

• Pricing for public projects (free): https://cirrus-ci.org/faq/#are-there-any-limits
• Available FreeBSD nodes (12.2-RELEASE, 13.0-ALPHA): https://cirrus-ci.org/faq/#are-there-any-limits

[AkihiroSuda]

cc @samuelkarp @dmcgowan @estesp

[koobs]

If you need support with setup/config, don't hesitate to ping

[AkihiroSuda]

Thanks!

[koobs]

For reference, requested image updates from Cirrus for better and greater coverage:

https://twitter.com/freebsdhelp/status/1384090389439598596?s=21

Edit: Cirrus are awesome and already have all the latest versions (automatically)

[samuelkarp]

I didn't know about Cirrus, but that looks like a good possibility. I've also opened #45 to track porting the unit tests, since right now they're Linux-only.

[emaste]

Cirrus lets you use any GCP image - the list is available using the gcloud CLI tool: gcloud compute images list --project freebsd-org-cloud-dev --no-standard-images

The FreeBSD base system CI story includes Cirrus-CI, you can see status at https://cirrus-ci.com/github/freebsd/freebsd-src/

@koobs is correct, Cirrus-CI is awesome.