Safety fix for #1879: do not raise an exception if setuptools hack fails to apply, but warn about it since it's unclear how to handle such a case.

Fix abs(long long) test in 32bit MSVC: need to calculate max value in Python as Cython assumes result to be Py_ssize_t (due to sizeof()), which is < sizeof(long long).

Configure another Cython option in test runner from *inside* the shard runner to support non-forking setups (i.e. Windows).

Configure Cython options in test runner from *inside* the shard runner to support non-forking setups (i.e. Windows).

More pypy3 fixes

Fixes a segfault on pypy3 due to the coroutine type missing tp_iternext in 5.8.

Last change accidentally disallowed mismatching 'nogil' assignments even when compatible. Reallow them, and clean up the last change a little.