[3.10] bpo-41498: Fix build on platforms without sigset_t (GH-29770) (GH-29773)



(cherry picked from commit dc19e8698327cae3d6274b73c135375955f1d0d0)


Co-authored-by: Christian Heimes <christian@python.org>

Automerge-Triggered-By: GH:tiran
5 files changed