Good question! It was merged quite close to the release, so it's hard to guess if it landed in beta already. So, let's have a look at [1]! And yep, it's in the beta branch.
This means it's in 1.23, which'll be released in 6 weeks.
Yes, once [1] lands, you can add it with `rustup target add wasm32-unknown-unknown` and then you can `cargo build --target=wasm32-unknown-unknown`.
You should note that it's not as simple as that, though. Depending on the context you want to run WASM you might need to do additional steps. E.g., when running this in a browser, you might not be able to use the std lib to spawn threads just yet.
This means it's in 1.23, which'll be released in 6 weeks.
[1]: https://github.com/rust-lang/rust/commits/beta