_global_shutdown_lock should be reinitialized in forked children

from imports

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In the case of multiprocessing.synchronize() being missing, the
test_concurrent_futures test suite now skips only the tests that
require multiprocessing.synchronize().

Validate that multiprocessing.synchronize exists as part of
_check_system_limits(), allowing ProcessPoolExecutor to raise
NotImplementedError during __init__, rather than crashing with
ImportError during __init__ when creating a lock imported from
multiprocessing.synchronize.

Use _check_system_limits() to disable tests of
ProcessPoolExecutor on systems without multiprocessing.synchronize.

Running the test suite without multiprocessing.synchronize reveals
that Lib/compileall.py crashes when it uses a ProcessPoolExecutor.
Therefore, change Lib/compileall.py to call _check_system_limits()
before creating the ProcessPoolExecutor.

Note that both Lib/compileall.py and Lib/test/test_compileall.py
were attempting to sanity-check ProcessPoolExecutor by expecting
ImportError. In multiprocessing.resource_tracker, sem_unlink() is also absent
on platforms where POSIX semaphores aren't available. Avoid using
sem_unlink() if it, too, does not exist.

Co-authored-by: Pablo Galindo <Pablogsal@gmail.com>

* Add cancel_futures parameter to the Executor base class, since it was missed in the original PR (https://github.com/python/cpython/pull/18057) that added cancel_futures.

Fix a race condition in concurrent.futures._ThreadWakeup: access to
_ThreadWakeup is now protected with the shutdown lock.

Process.shutdown(wait=True) of concurrent.futures now closes
explicitly the result queue.

Roughly based on https://github.com/python/cpython/commit/904e34d4e6b6007986dcc585d5c553ee8ae06f95, but with a few substantial differences.

/cc @pitrou @brianquinlan

- concurrent.futures
- ctypes
- http.cookies
- multiprocessing
- queue
- tempfile
- unittest.case
- urllib.parse