Enable -m test for wasi #4583

Requirements:

• add wasm32-wasi as wasi in sys.platform #4576
• Fix py_freeze! to run library with __main__ without __init__ #4581

Feature

Due to enhancement of wasi support of python libraries, we now also can do it!

How to

Build wasi binary:

cargo build --target wasm32-wasi --no-default-features --features freeze-stdlib,stdlib --release

You will need to install wasm32-wasi target using rustup.

Run test:

wasmer run --dir . target/wasm32-wasi/release/rustpython.wasm -- -m test test_support

You will need to install wasmtime or wasmer to run it.

Current result:

...
  File "test.support", line 16, in <module>
  File "unittest", line 66, in <module>
  File "unittest.main", line 8, in <module>
  File "unittest.runner", line 9, in <module>
  File "unittest.signals", line 1, in <module>
  File "signal", line 1, in <module>
ModuleNotFoundError: No module named '_signal'

It doesn't work. Because we don't have _signal module for wasi yet, while cpython does have.

To run cpython wasi build, I used this article as reference:
https://snarky.ca/testing-a-project-using-the-wasi-build-of-cpython-with-pytest/