Fix x11-toolkits/py-kivy due to cython update.

Cython changes its temporary variable handling and now fails on the file:

kivy/graphics/sahder/pyx

This has already been fixed upstream so just backport that fix.

Also, update the USE_PYTHON et al variables.

PR: 194065
Reported by: John Marino (marino@FreeBSD.org)
Obtained from: https://github.com/kivy/kivy/commit/b2bc566