[3.9] bpo-40777: Initialize PyDateTime_IsoCalendarDateType.tp_base at run-time (GH-20493) (GH-20495)



Recent changes to _datetimemodule broke compilation on mingw; see the comments in this change for details.

FWIW, @corona10: this issue is why `PyType_FromModuleAndSpec` & friends take the `bases` argument at run time.
(cherry picked from commit 459acc551656785bc4a3363d65c7a60f822da8e3)


Co-authored-by: Petr Viktorin <encukou@gmail.com>
2 files changed