bpo-40280: Misc fixes for wasm32-emscripten (GH-30722)

[tiran]

• skip tests when modules like fcntl or _multiprocessing are not available
• add missing check for fork
• grp and subinterpreter don't work on wasm32-emscripten node builds

https://bugs.python.org/issue40280

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 FreeBSD Non-Debug 3.x has failed when building commit c02e860.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/172/builds/1211) and take a look at the build logs.
4. Check if the failure is related to this commit (c02e860) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/172/builds/1211

Summary of the results of the build (if available):

== Tests result: ENV CHANGED ==

411 tests OK.

10 slowest tests:

• test_peg_generator: 9 min 25 sec
• test_multiprocessing_spawn: 4 min 47 sec
• test_concurrent_futures: 4 min 9 sec
• test_tokenize: 3 min 49 sec
• test_multiprocessing_fork: 3 min 1 sec
• test_unparse: 2 min 53 sec
• test_largefile: 2 min 33 sec
• test_asyncio: 2 min 21 sec
• test_multiprocessing_forkserver: 2 min 5 sec
• test_gdb: 1 min 46 sec

1 test altered the execution environment:
test_multiprocessing_spawn

20 tests skipped:
test_dbm_gnu test_devpoll test_epoll test_idle test_ioctl
test_msilib test_nis test_readline test_spwd test_startfile
test_tcl test_tix test_tk test_ttk_guionly test_ttk_textonly
test_turtle test_winconsoleio test_winreg test_winsound
test_zipfile64

Total duration: 22 min 31 sec

Click to see traceback logs

Traceback (most recent call last):
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-9e36.nondebug/build/Lib/multiprocessing/resource_tracker.py", line 209, in main
    cache[rtype].remove(name)
    ^^^^^^^^^^^^^^^^^^^^^^^^^
KeyError: '/psm_7fad03b8'