setup.py: Don't patch cython files, if not necessary

Signed-off-by: Michael Buesch <m@bues.ch>
setup.py: Don't build cython modules, when building wininst.

Signed-off-by: Michael Buesch <m@bues.ch>
setup.py: Add workaround for mbcs-bug

Signed-off-by: Michael Buesch <m@bues.ch>