misc lang/wasi-* fixes committed

[Tobias Nygren <tnn%NetBSD.org@localhost>]

Hi,

I've committed some fixes that hopefully fix these packages.
At least these issues should be fixed:

- error: <wasi/api.h> only supports wasm32
- "make replace" of wasi-libcxx fails

I will ask for pull-ups when the changes have baked for a bit.
Could people who had issues building Firefox due to this
please cvs up and report back if it is still broken?

Kind regards,
-Tobias