pykg-config build for 12.0/13.0

[dhomeier]

Compatibility with python3

[dmacks]

The existing package installs %p/bin/pykg-config.real that is an executable starting with #!/usr/bin/python. On platforms where we have /usr/bin/python3 instead, does that give python3 in the #! line? That's a .deb variation, so we'd need separate revisions on the different distros.

[dhomeier]

On Python3 systems it's

#!/Applications/Xcode.app/Contents/Developer/usr/bin/python3

and I actually thought the two would be pretty much exclusive, but it seems Python 3.8 was already made available in Catalina
https://discuss.python.org/t/right-or-best-way-to-install-python-in-macos-10-15-catalina/6204/2
while 2.7 was only finally pulled with the update to 12.3
https://developer.apple.com/documentation/macos-release-notes/macos-12_3-release-notes#Python
(which I assume already came with 3.9.6 installed).
The way the package is first checking for /usr/bin/python it would now still use 2.7 as long as it's available; would probably make more sense to use python3 throughout at least everywhere 3.9.6 is installed. So should this be split into two packages, dist-restricted to (12.0, 13.0) and the rest, respectively?