consider gating builds for osx passing tests

[eyberg]

osx is definitely a preferred target, albeit with it's warts, i think the nightlies are set to run on osx but not every build https://github.com/nanovms/ops/pull/733

[eyberg]

we do have ci builds for osx https://github.com/nanovms/ops/blob/master/.circleci/config.yml#L29 - not sure if this is necessary anymore?

[francescolavra]

Even though we have a "build-mac" CI job in config.yml, it's not being run at every commit, only the Linux build job is being run. We would need to specify the Mac build explicitly in the commit workflow, similar to what the Nanos config.yml file does; something like:

workflows:
  commit-workflow:
    jobs:
      - build
      - build-mac