[3.9] gh-101981: Build macOS as recommended by the devguide (GH-102070) by erlend-aasland · Pull Request #102186 · python/cpython

I was mystified why this change now seems to work for 3.9 after the lengthy testing and discussion here shows that it shouldn't. But further investigation shows that, just 3 days ago, Homebrew made a change to their tcl-tk formula so that their Tcl/Tk is no longer "keg-only", meaning it is now linked into their normal install locations and, thus, the non-functional (as explained in the link) PKG_CONFIG_PATH addition is no longer needed with this latest Homebrew update! Great timing. We should re-examine the devguide directions and this change in that light. I'll think about it.