The "musl" part of the Zig target triples `wasm32-wasi-musl` and
`wasm32-emscripten-musl` refers to the libc, not really the ABI.

For WASM, most LLVM-based tooling uses `wasm32-wasi`, which is
normalized into `wasm32-unknown-wasi`, with an implicit `-unknown` and
without `-musl`.

Similarly, Emscripten uses `wasm32-unknown-emscripten` without `-musl`.

By using `-unknown` instead of `-musl` we get better compatibility with
external tooling.