Allow WASI-less builds with --triple wasm32-unknown-unknown #2412
Description
Most probably depends on #2411, as ICU requires libc I guess? 🤔
Making this available as a separate triple allows us to ship both WASI-linked and WASI-less stdlib simultanously. Then people who need WASI (i.e. everyone who needs Foundation for example) can build with existing --triple wasm32-unknown-wasi, while --triple wasm32-unknown-unknown is available as an option for slim builds that don't need Foundation.