ci(test-os): cross build freebsd binaries using the Dockerfile

[crazy-max]

follow-up #4180

[tonistiigi]

cc @akhramov

[tonistiigi]

Not directly related to this PR but for my better understanding: what it the value of

I also can't see integration tests for freebsd. If they are missing, don't add in this PR but if I just don't know where to look then you can comment here.

[crazy-max]

Not directly related to this PR but for my better understanding: what it the value of

If the remote vagrant box has been updated it will take some time to export the cache:

But consecutive builds will be faster if it has not changed:

I also can't see integration tests for freebsd. If they are missing, don't add in this PR but if I just don't know where to look then you can comment here.

Indeed we don't run integration tests atm (just smoke one running a Dockerfile). We could probably have a similar matrix to

buildkit/.github/workflows/buildkit.yml

Lines 33 to 54 in 12bbf07

	uses: ./.github/workflows/.test.yml
	with:
	cache_scope: build-integration-tests
	pkgs: ./client ./cmd/buildctl ./worker/containerd ./solver ./frontend
	kinds: integration
	codecov_flags: core
	includes: |
	- pkg: ./...
	skip-integration-tests: 1
	typ: integration gateway
	- pkg: ./client
	worker: containerd
	tags: nydus
	typ: integration
	- pkg: ./client
	worker: oci
	tags: nydus
	typ: integration
	- pkg: ./...
	tags: nydus
	skip-integration-tests: 1
	typ: integration

running inside the vagrant box. Don't think we can use a freebsd variant for our integration tests image though.