That would go in the Nim std lib - an `--os:wasi` or some bindgen macros like here: [https://hacks.mozilla.org/2018/04/javascript-to-rust-and-back-again-a-wasm-bindgen-tale](https://hacks.mozilla.org/2018/04/javascript-to-rust-and-back-again-a-wasm-bindgen-tale)/ \- wasm-bindgen is apparently pluggable so it's possible to marshal other languages than rust.
Clearly upstream Nim stuff and not part of nlvm :)
