gh-90473: Skip and document more failing tests on WASI (GH-93436)

- Mark more ``umask()`` cases
- ``dup()`` is not supported
- ``/dev/null`` is not available
- document missing features
- mark more modules as not available

Lib/test/test_compileall.py

@@ -434,6 +434,9 @@ class CompileallTestsWithoutSourceEpoch(CompileallTestsBase,
     pass
 
 
+# WASI does not have a temp directory and uses cwd instead. The cwd contains
+# non-ASCII chars, so _walk_dir() fails to encode self.directory.
+@unittest.skipIf(support.is_wasi, "tempdir is not encodable on WASI")
 class EncodingTest(unittest.TestCase):
     """Issue 6716: compileall should escape source code when printing errors
     to stdout."""