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

[Changqing Jing via cfe-commits]

Changqing-JING wrote:

@dschuff @sbc100 
Thanks, I agree that exposing arbitrary wasm-opt arguments would make Clang
depend on wasm-opt's CLI and make the interaction with the existing optimization
pipeline unclear.

Would it be preferable to replace this proposal with an option to disable
Clang's automatic wasm-opt invocation? Users needing a non-default Binaryen
feature set or pass pipeline could then invoke wasm-opt separately, while the
default Clang behavior continues to use the target_features section.

Does that sound like the intended direction?

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