Document Compiling a New C/C++ Module to WebAssembly with WASI

[kzhsw]

In page Compiling a New C/C++ Module to WebAssembly, Emscripten SDK was chosen. The WASI sdk is also possible to compile many C/C++ Module with a standardized system interface and less js glue code, maybe this can also be documented here.

[bsmth]

Thanks for raising. I think it's better to track in a content issue here: mdn/content#37587 so I'm closing this for now.