[llvm] Ensure NoTrapAfterNoreturn is false for the wasm backend (PR #65876)

[Matt Harding via llvm-commits]

majaha wrote:

> Yeah I get that we haven't been warning about a similar case (--trap-unreachable) before. But I think they are more of what ended up happen, and not the firm intention not to warn for conflicted requests.
>
> For example, that --trap-unreachable command line option was added much later (https://github.com/llvm/llvm-project/commit/6d9f8c98172cd4d648e33b21679325227c5cec83) than when we set it to false (https://github.com/llvm/llvm-project/commit/ffa143ce814101fb1277ba65b20bdf86775d0b32). When first we set it to false in 2015, that option didn't exist so we had nothing to warn against. And someone who added that option in 2018 didn't go through all the code to check if there were any conflicting assignments.

You might be right, but my feeling is that the behaviour of `--trap-unreachable` and `--no-trap-after-noreturn` should be consistent across all backends, and probably with other options too. I think that's a big enough change to warrant discussion and testing separately.

This change is consistent with the current behaviour and fixes a real issue, so I think it makes sense for this change to go in first, before we start to think about changing any existing behaviour.

https://github.com/llvm/llvm-project/pull/65876