Make writing to stdout and stderr not crash #2

We're using --stub-wasi at the moment, which means things like fd_write are coded to immediately trap. Quit that. stdout and stderr not being in the preopens may also be a barrier; adding those should be possible with changes to Viceroy.

It may be possible and desirable to monkeypatch in Python to redirect stdout and stderr to a logging endpoint, though our initial attempts were unsuccessful.