bpo-40280: Block more non-working syscalls in Emscripten (GH-31757)

- getgroups always fails.
- geteuid and getegid always return 0 (root), which confuse tarfile and
  tests.
- hardlinks (link, linkat) always fails.
- non-encodable file names are not supported by NODERAWFS layer.
- mark more tests with dependency on subprocess and multiprocessing.
  Mocking does not work if the module fails to import.

Lib/test/test_script_helper.py

@@ -3,7 +3,7 @@
 import subprocess
 import sys
 import os
-from test.support import script_helper
+from test.support import script_helper, requires_subprocess
 import unittest
 from unittest import mock
 
@@ -69,6 +69,7 @@ class TestScriptHelper(unittest.TestCase):
             self.assertNotIn('-E', popen_command)
 
 
+@requires_subprocess()
 class TestScriptHelperEnvironment(unittest.TestCase):
     """Code coverage for interpreter_requires_environment()."""