Re-enable WASM CI after #1047

[lqd]

In #1047 we've noticed the WASM CI starting to fail for reasons seemingly unrelated to the PR:

Error: failed to run main module `/checkout/target/wasm32-wasi/release/deps/core_arch-c0d11357b68974c7.wasm`

Caused by:
    0: failed to instantiate "/checkout/target/wasm32-wasi/release/deps/core_arch-c0d11357b68974c7.wasm"
    1: unknown import: `env::llvm.wasm.widen.low.signed.v8i16.v16i8` has not been defined

rustc updated to LLVM12 around the same time so it may be related.

#1047 will temporarily disable WASM CI when it lands, and this issue tracks the need to re-enable it once we've diagnosed and fixed the issue.

[Amanieu]

cc @alexcrichton

[alexcrichton]

Thanks for the heads up!

This is likely to be disabled for awhile (but that's fine of course). The wasm simd spec has recently reached a stable-ish point but it meant that all the opcodes were renamed. Once LLVM has sync'd to the current version of the spec I'll work on implementing it all in Rust (probably backporting patches and then updating the implementation of all of the intrinsics).

[alexcrichton]

I think this is probably ok to close now?