Pipe read() never blocks, and poll() ignores timeouts

I have run into serious issues that make communication between pthreads, completely off the browser or main thread, totally broken. First is that read() on a pipe that should be blocking, instead returns immediately. And second, poll ignores its timeout parameter and also returns immediately.

This has been a persistent issue that seems to be ignored:

#25759, #20615, #19447, #16704, #16047

I am creating a new issue hoping for some attention to this issue. Now that JSPI and pthreads are available, I don't think there's any reason not to implement this correctly.

Start by reproducing the pthreads-only behavior of blocking pipe read() and poll() with JSPI enabled, then trace the read() and poll() entry points and compare the related issues #25759, #20615, #19447, #16704, and #16047. Done means pipe read() blocks as expected and poll() honors its timeout instead of returning immediately.

Written by the indexing model from the issue text.