Fix Windows builds in CI

[mathewhodson]

This resolves the following error when building 'pywatchman.bser' extension:

error: Microsoft Visual C++ 14.0 or greater is required. Get it with "Microsoft C++ Build Tools": https://visualstudio.microsoft.com/visual-cpp-build-tools/

[fanzeyi]

Hi!

Thanks for looking into this. I spent some time a few weeks ago trying to fix this as well but I wasn't able to find the root case. Here are my findings in case its useful:

• If I directly build the Python package with python setup.py on GitHub Windows environment, it works. (run, commit).
• If I remove all the CMake stuff and most of the dependencies, it works. (run, commit)
• If I only remove the CMake changes but still let getdeps build the dependencies, it fails. (run, commit)

You can find all my attempts at https://github.com/fanzeyi/watchman/actions?query=branch%3Afix-windows-ci++. I do amend and force push all the time so you will have to click on the commit id in the run to see what changes I made.

I suspect somehow having the dependencies messed up setuptools's logic to locate MSVC but I wasn't sure why. Hope this will be helpful. Let me know if you have any questions.