Fix wasi_polloneoff on Windows

[MarkMcCaskey]

We're missing wasi_polloneoff on Windows. It's a bit tricky, but maybe we can get it working well enough to run applications that need to sleep.

See also #1971, #570

[nlewycky]

Is there a spec document for this function?

[Hywan]

The only reference to wasi_polloneoff that Google or Ecosia or other search engines found is… this issue :-D.

Maybe this https://github.com/WebAssembly/WASI/blob/96c202b046e28d215c64d3a558566141d8efd8b9/phases/ephemeral/witx/wasi_ephemeral_poll.witx?

[MarkMcCaskey]

Is there a spec document for this function?

In general, no. There's https://github.com/WebAssembly/WASI/blob/main/phases/snapshot/docs.md#poll_oneoff which is a description of the function and its parameters but it doesn't get into much real detail.

If you care about being precise, you can read the WASI libc code but that's not particularly easy. Most of our WASI calls have been developed by reading the docs I linked above and working with Wasm modules that use that syscall until they appear to behave correctly.

There's on-going talks about creating standardized spec tests for WASI though, so I think that'll go a long way towards improving consistency in implementations

[syrusakbary]

Closing this in favor of #570