ci: Run 'make distcheck' on FreeBSD

The Cirrus CI integration was modeled after the Travis CI jobs,
but those were limited to macOS where the test suite is currently
still broken. FreeBSD can run the full distcheck just fine, so
let's do that.

Fixes: 6190c141
Signed-off-by: Andrea Bolognani <abologna@redhat.com>
5 jobs for freebsd-distcheck in 32 minutes and 20 seconds (queued for 1 second)