Looks like this is available (since Go 1.21 [0]), so no need to build from source anymore. Just did a quick 'hello world' test to verify and it worked:
GOOS=wasip1 GOARCH=wasm go build -o main.wasm main.go
wasmtime main.wasm
If you're interested in wasm/wasi and niche hardware with Go, you should check out TinyGo [1] if you haven't already.
[0] https://go.dev/blog/wasi
[1] https://tinygo.org/docs/guides/webassembly/wasi/