Recognize the "wasm32-wasi" target tuple.

[sunfishcode]

To minimize confusion with multiarch tuples which omit the vendor field of the target tuple, and to save a small amount of typing, we're preparing to switch the "wasm32-unknown-wasi" target to be spelled "wasm32-wasi". LLVM already accepts both forms. This is similar to how the vendor field is omitted in rustc tuples such as "x86_64-fuchsia" and "aarch64-linux-android".

The patch here just changes the cc-rs crate to recognize either form in anticipation of this change.

[alexcrichton]

I think that this target here is the one passed to TARGET which is in turn passed to rustc, and rustc doesn't currently accept wasm32-wasi (that's a whole separate discussion...), so I'm not sure that this'll actually ever get exercised? Did this show up in practice though?

[sunfishcode]

rust-lang/rust#60585 has now landed and is in the latest nightly builds, so wasm32-unknown-wasi is now wasm32-wasi.

[alexcrichton]

👍