[Build] Another attempt at building Python 3.9 MacOS wheels

[mwtian]

Why are these changes needed?

I was able to reproduce the issue of Python 3.9 wheels missing ray/python/ray/thirdparty_files on my MacBook. IIUC, the file copying logic in python/setup.py is broken in some cases. Logic in distutils.build_ext actually copied the psutil and setproctitle files. This behavior could have changed on MacOS Python 3.9, for these types of files. Fixing the logic in setup.py seem to fix the issue.

A more radical approach would be to not vendor psutil and setproctitle anymore, and require users to install themselves as Python dependencies. If Ray C++ uses these libraries, they could (might already?) be statically linked.

Related issue number

#11287

Checks

• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • Unit tests
  • CI tests
  • Release tests
  • This PR is not tested :(

[wuisawesome]

Seems fine, let's wait until morning to merge it though, since the other attempts also looked fine until they broke master 😛

[mwtian]

Fixed an issue in setup.py and reverted the change in build-wheel-macos.sh. MacOS Py 3.9 wheel passes validation: https://travis-ci.com/github/ray-project/ray/jobs/512659322#L34378-L34457

[wuisawesome]

crossing fingers and merging now 🤞

[wuisawesome]

This might've worked? There were some travis CI issues today, so we're 1/2 on the mac wheel builds. The failed build was due to a timeout (this also happened before thought). I'm cautiously excited, but we may need to make sure the mac wheel build doesn't timeout too often.

[mwtian]

Yes, I hope it works too! From my observation, it seems every time we run out then refill Travis credits, all Bazel deps are rebuilt which can longer time. Hopefully we will see faster Mac builds tonight!