Promote -Wcast-function-type to an error in builds. (#46356)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46356
Adding the flag `-Werror=cast-function-type` to ensure we don't allow
any invalid casts (ex: PyCFunction casts).
For more details see: https://github.com/pytorch/pytorch/issues/45419
ghstack-source-id: 114632980
Test Plan: waitforbuildbot
Reviewed By: albanD
Differential Revision: D24319759
fbshipit-source-id: 26ce4650c220e8e9dd3550245f214c7e6c21a5dc
