Enable PYTHON_SYS_EXECUTABLE

[KoichiYasuoka]

No description provided.

[davidhewitt]

Thanks for the PR! Can you please add a little detail in what situation you need this functionality?

As I understand, with setuptools-rust we are installing the Rust extension to be run with sys.executable. I worry that enabling these environment variables could cause installations to be built incorrectly.

[KoichiYasuoka]

I often use setuptools-rust on Cygwin, where the sys.executable is /usr/bin/python3.7. But in rust (Windows) view the executable file is C:\cygwin64\bin\PYTHON~1.EXE, so I use PYTHON_SYS_EXECUTABLE to tell rust where the executable file is.

[davidhewitt]

Ah, I see - that makes sense. It's a bit of a weird case; I agree that what you're doing is the right solution.

FYI these days I use WSL 2 instead of Cygwin on Windows, which I find works very very nicely and is a bit friendlier to use than Cygwin 😄

I'm going to just push a CHANGELOG entry to this branch, and then I'll merge. Thanks very much for your contribution!