missing host-fn support for multi-value

[marxin]

Right now, the multi-value support is not properly covered when it comes to host function that return multiple arguments, e.g. (i32, i32, i32) in Rust language.

More precisely, we're missing the full support for Singlepass, Cranelift and the LLVM+Windows targets. The #5936 PR included intensive set of tests that stress the functionality (LLVM+linux and LLVM+macos-arm work correctly).

For the Cranelift, we have to implement the ABI ourselves (using StructReturn type¹), similarly to what we do for LLVM: https://github.com/wasmerio/wasmer/blob/main/lib/compiler-llvm/src/abi/x86_64_systemv.rs.

Footnotes

1. https://docs.rs/alexcrichton-cranelift-codegen/latest/cranelift_codegen/ir/enum.ArgumentPurpose.html#variant.StructReturn ↩