xcb-proto: backport fix for python gcd function

xcb-proto: backport fix for python gcd function

This backports the fix [1] for the following build error for nativesdk on
Fedora 33 which is caused by the removal of fractions.gcd() in favor of
math.gcd() in python 3.9 [2]:

ImportError: cannot import name 'gcd' from 'fractions' (/usr/lib64/python3.9/fractions.py)

[1] https://gitlab.freedesktop.org/xorg/proto/xcbproto/-/commit/426ae35bee1fa0fdb8b5120b1dcd20cee6e34512
[2] https://bugs.python.org/issue39350

Signed-off-by: Richard Leitner <richard.leitner@skidata.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>