In #128628 I switched the way of handling function pointer casts in emscripten to an approach based on wasm-gc. Unlike the previous approaches this should work on the wasi targets, at least the ones that include wasm-gc. There's some difficulty in that there's no support for the instructions in the clang C front end, nor really in the backend yet. So I'm not sure what is the best way to emit these instructions. We only would need to generate one short function using them though.

@brettcannon WDYT?