https://bugs.winehq.org/show_bug.cgi?id=42474
--- Comment #15 from Sebastian Ernst ernst@pleiszenburg.de --- Looks like "PathCchCombineEx" really is Windows 8 and above only. The odd things is though that Python 3.6 should explicitly support Windows Vista and 7. This API-call therefore should not exist.
I opened a bug against CPython seeking clarification: http://bugs.python.org/issue30186