a) NoneType object is not iterable. If the function don't return empty list later distutil will fail on the lines like  libraries.extend(self.dll_libraries)

b) method for detection of a msvc runtime is not correct. If the method return a library GCC will link to two c-runtimes. Also some function dearation are not visible if is not specified appropriate preprocessor directive.

So I could not found reason this method to exist .