bpo-37685: Fixed comparisons of datetime.timedelta and datetime.timezone. (GH-14996)

bpo-37685: Fixed comparisons of datetime.timedelta and datetime.timezone. (GH-14996)

There was a discrepancy between the Python and C implementations.

Add singletons ALWAYS_EQ, LARGEST and SMALLEST in test.support
to test mixed type comparison.
(cherry picked from commit 17e52649c0e7e9389f1cc2444a53f059e24e6bca)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>