Check poll timeout (buggy in browser)

[nampereira]

poll() does not correctly timeout (on the browser). Either some problem with my poll calls, or in wasi implementation (libc bottom half, or wasi browser implementation).

Libc bottom half here:
https://github.com/WebAssembly/wasi-libc/blob/5a7ba74c1959691d79580a1c3f4d94bca94bab8e/libc-bottom-half/cloudlibc/src/libc/poll/poll.c

WASMER WASI browser implementation (poll_oneoff):
https://github.com/wasmerio/wasmer-js/blob/master/packages/wasi/src/index.ts