Rust supports wasm32-unknown-unknown target now

[bennyyip]

See rust-lang/rust#45905 and https://www.hellorust.com/setup/wasm-target/.
FYI, https://github.com/alexcrichton/wasm-gc may reduce the output size.

[dtysky]

Thanks for your suggestion, but after trying:

wasm-gc src/rust-es/test.wasm src/rust-es/test1.wasm

I found the size of wasm file did not change a bit.

I think the reason of a huge size of output wasm file and js file is: rustc does not pass any options to emcc, so emcc will generate codes with default options (include all runtime code).

[dtysky]

Sorry...it looks I misunderstand what you say.
I will add the usage of wasm-unknown-unknown to this guide tomorrow.

Thanks.