How to use posix threads?

Hi there, FastLED core dev here.

I wanted to bring this up in a bug report because it seems that there is a lack of information about how to bring up posix threads as detailed here:

https://emscripten.org/docs/porting/networking.html#full-posix-sockets-over-websocket-proxy-server

In this document it shows thatt there is a program here:

https://github.com/emscripten-core/emscripten/blob/main/tools/websocket_to_posix_proxy/src/main.cpp

May I assume that my task is to download and compile this main program into my code base?

What other settings are necessary for this to run? There's a lot of missing information. Yes I put AI on it and it couldn't figure it out either. Are there examples that show how to integrate this? I'm sure I'm doing it wrong.