Incorrect @wasmMemoryGrow codegen for wasm64 target

[rdunnington]

Zig Version

0.12.0

Steps to Reproduce and Observed Behavior

With this program memtest.zig:

const KB = 1024;
const MB = 1024 * KB;
const GB = 1024 * MB;

const PAGE_SIZE = 64 * KB;
const PAGES_PER_GB = GB / PAGE_SIZE;

export fn memtest() void {
    _ = @wasmMemoryGrow(0, PAGES_PER_GB * 8);
}

Building with the command:
zig build-exe memtest.zig -target wasm64-freestanding -fno-entry --export=memtest -O ReleaseSmall

Yields the codegen (translated with wasm2wat --enable-all --no-check memtest.wasm:

(module
  (type (;0;) (func))
  (func (;0;) (type 0)
    i32.const 131072
    memory.grow
    drop)
  (memory (;0;) i64 16)
  (global (;0;) (mut i64) (i64.const 1048576))
  (export "memory" (memory 0))
  (export "memtest" (func 0)))

Running wasm2wat --enable-all memtest.wasm (without the --no-check) yields an error:

memtest.wasm:0000043: error: type mismatch in memory.grow, expected [i64] but got [i32]

Note that an i32 is being pushed on the stack instead of an i64, even though the memory type is declared as i64.

Expected Behavior

An i64 is pushed to the stack instead of i32 in accordance with the memory64 spec proposal:

https://github.com/WebAssembly/memory64/blob/main/proposals/memory64/Overview.md

All memory instructions are changed to use the index type, and the offset must also be in range of the index type