[windows] fix missing environment variables when running check-lldb

[charles-zablit]

Currently when running build.ps1 at desk to build and test LLDB, the tests will fail because python39.dll is not in the Path and because PYTHONHOME is not set.

This PR adds python39.dll to the Path before running the tests and passes PYTHONHOME to lit through LLDB_TEST_USER_ARGS. Simply setting the PYTHONHOME env variable is not enough as lit reset the env before running the tests.

[charles-zablit]

@swift-ci please test

[JDevlieghere]

This makes sense. I think passing PYTHONHOME should be meaningful on all platforms, so instead of doing this in build.ps1, I think we can do this upstream, and have CMake configure that property in lit.site.cfg.in, similar to config.python_executable.

Not only does that avoid diverging the platforms and swift repo, it also has the benefit of being a bit more "hermetical" if the test python is different. I'm not sure if this is even possible here, but build-script for example often runs under a different python than what we build lldb against.

[charles-zablit]

I opened llvm/llvm-project#143183 with the changes to the lldb lit config. We still need the env:Path change in this patch for lldb to correctly find python.dll. Or maybe we want to do that in lit as well?

[compnerd]

I opened llvm/llvm-project#143183 with the changes to the lldb lit config. We still need the env:Path change in this patch for lldb to correctly find python.dll. Or maybe we want to do that in lit as well?

I think that is best handled outside of lit - this location is something specific to the build setup. It is possible to place the extracted python anywhere. If we want to do this through lit, it should be wired through CMake and through CMake into lit.

[charles-zablit]

I think that is best handled outside of lit - this location is something specific to the build setup. It is possible to place the extracted python anywhere. If we want to do this through lit, it should be wired through CMake and through CMake into lit.

What I have in mind is to do something like this:

# lit.cfg.py
config.environment["PATH"] = os.path.pathsep.join(config.python_root_dir, config.environment.get("PATH", ""))

And config.python_root_dir is the CMake variable Python3_ROOT_DIR.
This would mean that the setting is wired through CMake and then through lit.

What do you think?