[openmp][WebAssembly] Add support for wasm64 (#181669)

Building on the existing ability to build wasm32, this change mostly
redefines `M_ARCH_WASM` to `M_ARCH_WASM32` and then introduces
`M_ARCH_WASM64` based on `__wasm64__` define

GitOrigin-RevId: 019fc9efa2dc8f36d9b4794caeca0738a06db667