`umask`ed `os.makedirs()` sometimes fails on Emscripten

[freakboy3742]

Bug report

Bug description:

When os.umask is used on a os.makedirs() call, the permissions aren't always honoured:

os.umask(0o002)
os.makedirs("./dir1/dir2")
print(os.stat("./dir1").st_mode & 0o777)

Should return 0o775; but returns 0o755 on some installs.

This can be observed as a failure of test_os.MakedirTests.test_mode. The Emscripten buildbot fails consistently on this; it also fails on my macOS machine. However, @hoodmane has been unable to reproduce it. The test has been skipped as part of #127146 to get a passing buildbot; more investigation is required.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Other