[llvm] [WebAssembly] avoid to enable explicit disabled feature (PR #80094)

[Congcong Cai via llvm-commits]

HerrCai0907 wrote:

>  I think it would be good to have the feature enabled in that case.

I think it should throw diagnose or assert it won't happen. Otherwise the user will find they disable some feature but code still has this feature.

https://github.com/llvm/llvm-project/pull/80094