[WIP] bpo-41713: Move _signal variables into a state structure by vstinner · Pull Request #23318 · python/cpython

* Set volatile keyword on structure members, rather than on the whole
  structure.
* PyInit__signal() now checks for CreateEvent() failure.
* On Windows, PyOS_FiniInterrupts() now closes sigint_event.
* Clear ItimerError at exit.
* Remove PyOS_InitInterrupts() from the public C API.