Issue7713 is not the same: it asks for a way to affect the hardcoded paths in setup.py, this issue asks to honor the SDK-root by setup.py.

I've done some further research and this affects distutils in general: the compiler has methods to look for files and those need to honor the SDK root as well.

The hard part will be to describe correctly how Apple's compilers behave when -isysroot is present. Replicating that in our build environment should then be straightforward.   The reason that the specification part is hard is that Apple's document don't fully describe how -isysroot works. That is, '-isysroot,/Some/SDK -I/Users/ronald/OpenSource' works and will look in /Users/ronald/OpenSource, even though '/Users' is not in the SDK directory. This means it is just prepending $UNIVERSALSDK to every filename is not a correct fix.