Avoid using setuptools shim of distutils

[charliermarsh]

Summary

It turns out that setuptools includes a shim to patch distutils. I'll admit that I don't fully understand why or how it's different, but this is the trick pip uses to ensure that it gets the "original" distutils.

We actually use distutils in two places: once for the system Python scheme, and once for virtual environments. In virtualenv, they do use the patched distutils, so this could deviate in ways I don't understand.

Closes #2302.

[charliermarsh]

@gaborbernat - do you know if it's necessary for virtualenv to use the patched version of distutils? I see a note in pypa/virtualenv#1771, but I can't tell if it's required or merely necessary for others that might import virtualenv.

[potiuk]

Nice!

[gaborbernat]

I believe this aligns with how packages behave. pip uses setuptools distutils historically for installing packages. So without that shim you might end up with bug reports of installations ending up in expected locations when the OS patched distutils and setuptools distutils information differs (primarily in debian).