GCC complains:

Python/pylifecycle.c: In function ‘_Py_InitializeFromConfig’:
Python/pylifecycle.c:900:13: warning: ‘interp’ may be used uninitialized in this function [-Wmaybe-uninitialized]
         err = _Py_InitializeMainInterpreter(interp, &main_config);
         ~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This seems spurious since &interp is passed to _Py_InitializeCore. Anyway, we
can easily initialize to quiet the warning.

This docstring has drifted since python2: https://github.com/python/cpython/blob/ca079a3ea30098aff3197c559a0e32d42dda6d84/Lib/encodings/__init__.py#L68

When subprocess.Popen() stdin= stdout= or stderr= handles are specified
and appear in pass_fds=, don't close the original fds after dup'ing them.

This implementation and unittest primarily came from @izbyshev (see the PR)

See also https://github.com/izbyshev/cpython/commit/b89b52f28490b69142d5c061604b3a3989cec66c

This also removes the old manual p2cread, c2pwrite, and errwrite closing logic
as inheritable flags and _close_open_fds takes care of that properly today without special treatment.

This code is within child_exec() where it is the only thread so there is no
race condition between the dup and _Py_set_inheritable_async_safe call.

Check for functionality via imports rather than checking sys.platform
specifically for Windows

* bpo-33217: Raise TypeError for non-Enum lookups in Enums

HMAC's digestmod was deprecated marked for removal, this removes it as planned.