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

[Sam Clegg via cfe-commits]

sbc100 wrote:

> But `--no-trap-after-noreturn` didn't exist before, so there was no way to specify that from the command line. You _created_ it, originally in this PR, and then the split-off PR in #67051. If this is a bugfix, it sounds like you are fixing a bug of your own making.

I think perhaps the misunderstanding here is that `NoTrapAfterNoreturn` was usable/settable by compilers such as rust via the LLVM API, even though `--no-trap-after-noreturn` didn't exist in llvm itself?

So adding this option just allows us to test something that wasn't testable, but was exposed via the API?  Is that right?

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