[llvm] Fix performance bug in buildLocationList (PR #109343)

[Sriraman Tallam via llvm-commits]

tmsri wrote:

> This continued to bug me a bit, so I put some traps on the `return false` paths at the end of `buildLocationList` with this PR and didn't get any test failures when running `ninja check-llvm`. Sorry to ask for more, but a test that covers that path would really help my understanding.
> 
> [jmorse at 7b78ea8](https://github.com/jmorse/llvm-project/commit/7b78ea87febc00b77ce8000659f61288c531eb09) <--- based on [11a5026](https://github.com/llvm/llvm-project/commit/11a50269e82b6dce49249c5cbe3a989b06f0848f) with the addition of some x86 traps, which should cause tests covering those paths to fail.

Ah nice!, let me see if I can make a test for this.

https://github.com/llvm/llvm-project/pull/109343