ThreadSantizer impl for emscripten

[michaelkremenetsky]

Couple months ago I spending a lot of time dealing with thread safety issues and wanted to get ThreadSantizer running on top of emscripten so I came up with this and only had the time to open source it now:
https://github.com/michaelkremenetsky/webtsan

I think alot of people here would find this interesting.

The main thing preventing it from being practically useful is that real-world WASM libcs like emscripten and wasi-libc need to be patched, as they currently cause a lot of false positives because they are not written with being run through a thread sanitizer in mind. I already tried patching it and realized how much work that was going to be.