Winch atomic loads x64

[MarinPostma]

this PR enable the thread feature for x64 in Winch, and implements atomic loads. This includes:

• i32.atomic.load8_u
• i32.atomic.load16_u
• i32.atomic.load
• i64.atomic.load8_u
• i64.atomic.load16_u
• i64.atomic.load32_u
• i64.atomic.load

It also enabled shared memory for winch.

#9734

reopened from #9954 because the branch was wrong

[cfallin]

Rather than a bool, which can be error-prone, could you define a small enum WasmLoadKind { Regular, Atomic } or similar and match on it in this function?

[saulecabrera]

Could you return a proper CodeGenError instead of panicking? I'm in the process of enabling spec tests for aarch64, in general recoverable errors are preferred as it makes it easier to define when a particular proposal is not fully supported in a particular backend (like threads in aarch64)

I believe we have CodeGenError::unimplemented_masm_instruction()

[saulecabrera]

Given this comment and for the purposes of this pull request, I wonder if it's necessary to introduce a new method in the MacroAssembler. I'd prefer if possible, if we could instead extend the current load definition to take in a load_kind argument, which categorizes if the load is atomic or not, similar to Chris' comment in https://github.com/bytecodealliance/wasmtime/pull/9970/files#r1909577300, that would also simplify the indirection happening in the CodeGen module:

We could simplify to:

• Extending emit_wasm_load to take in a load kind
• Performing the right dispatch directly from that method to the MacroAssembler, by passing the in-scope load kind.

[MarinPostma]

sure i'll do that

[MarinPostma]

comments addressed

[MarinPostma]

I'll fix the test tommorow.

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[MarinPostma]

I have enabled shared memory in winch, and updated the spec tests

[saulecabrera]

Thanks!