This is because of the _Py_fstat change to use errno instead of GetLastError. It seems other callers are relying on GetLastError to raise the correct exception, and that seems to be the standard throughout posixmodule as far as stat calls are concerned.

Best immediate fix is to revert back to how _Py_fstat was originally and update the caller's error handling, which I'll do now. Feel free to propose a more thorough patch that will unify error number handling, but I don't think it's a such a big problem.