Deprecate `sysconfig.expand_makefile_vars`

[FFY00]

Feature or enhancement

Proposal:

This function has been broken since v3.13.0a1 (see GH-128978), and nobody noticed. It was originally meant to posteriorly expand the values from sysconfig.get_paths(..., expand=False), which achieves the same as passing a custom vars argument to sysconfig.get_paths, a function that is actually tested.

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

GH-128978

[tomasr8]

There's already an issue for it :) #129064

[FFY00]

Ah, @tomasr8 thanks for noticing! 😊