Support configure macOS universal2 build with ARCHFLAGS

[messense]

See PyO3/setuptools-rust#115 (review)

[konstin]

Sorry, I don't fully understand what ARCHFLAGS does. Is the idea that you can somehow request a target architecture through that and do you have an example on how one would use that?

[messense]

Sorry, I don't fully understand what ARCHFLAGS does. Is the idea that you can somehow request a target architecture through that and do you have an example on how one would use that?

That's right. You can use ARCHFLAGS to tell C/C++ compiler to build for multiple architectures. For example ARCHFLAGS="-arch x86_64 -arch arm64" instruct compiler to build for both x86_64 & arm64.

https://github.com/python/cpython/blob/a5ed2fe0eedefa1649aa93ee74a0bafc8e628a10/Lib/_osx_support.py#L260

[messense]

Basically ARCHFLAGS make it consistent with C/C++ way of creating multiarch binary, also consistent with setuptools-rust and cibuildwheel. If rustc/cargo can produce universal macos binary in the future, I think they might want to use it too to play nice with C dependencies.

[konstin]

Ah, that's cool!