build(emscripten): omit unix/posix-poll.c for emscripten targets

[Rawan10101]

This change removes unix/posix-poll.c from the Emscripten source list. The file provides the POSIX-based implementation of uv__io_poll(), which is not directly usable in Emscripten's event-driven WASM environment. So, excluding it allows Emscripten targets to provide their own platform specific implementation of uv__io_poll() without symbol conflicts.

[torque]

If it doesn't work, then it makes sense to get rid of it, but I wonder if the libuv maintainers would be receptive to merging an upstream implementation of an emscripten compatible event loop so that every downstream user doesn't have to implement it themselves.

[Rawan10101]

If it doesn't work, then it makes sense to get rid of it, but I wonder if the libuv maintainers would be receptive to merging an upstream implementation of an emscripten compatible event loop so that every downstream user doesn't have to implement it themselves.

I was wondering about this as well. I can open an issue to raise the concern and get feedback from the maintainers.