All libffi tests pass now. The only failing ctypes test is test_callback_too_many_args which doesn't segfault anymore, it only soft fails. Planning to submit a PR to cpython that fixes test_callback_too_many_args.
See also:
bugs.python.org/issue47208
https://github.com/emscripten-core/emscripten/pull/16658
Hood Chatham