GH-92584: Redirect to Setuptools' guidance on extension modules by AA-Turner · Pull Request #108030 · python/cpython

I'm unsure if we should just drop extending/windows entirely

It's got important information in there that probably doesn't officially exist anywhere else, and for POSIX devs trying to make stuff work on Windows I'm sure it's invaluable (though it would be nice to have similar guides for Windows devs trying to make stuff work on *nix, but I'm not going to hold my breath). Expecting people to extract the same information from setuptools or another backend is asking too much.

That said, it's in desperate need of cleanup and modernisation anyway, so I won't miss it. A cross-platform primer on building extension modules by hand (i.e. without setuptools), referencing sysconfig heavily I'd expect, would be a great replacement.