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

[Matt Harding via llvm-commits]

majaha wrote:

As an aside, here's a thought that occurred to me while reading through the code: It would be nice if LLVM IR's `unreachable` was instruction-selected to an ISD::UNDEFINED_BEHAVIOUR pseudo-instruction (when TrapUnreachable is off). Physical ISA backends would lower it to nothing, but wasm could lower it to wasm `unreachable` or nothing, depending on what was needed to fulfil the stack requirement. I didn't feel brave enough to attempt that though :)

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