[clang] [clang][WebAssembly] Add WebAssembly wasm-opt configuration option (PR #222519)

[Sam Clegg via cfe-commits]

sbc100 wrote:

For users that want to do complete/non-default things with wasm-opt, perhaps it would be best to do that separately.  

IIRC several users have complained about the semi-automatic way that wasm-opt is run here.  Perhaps the best thing to do is enable it do be disabled, so it can be run separately (or not at all) from clang.

https://github.com/llvm/llvm-project/pull/222519