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

[Jeremy Morse via llvm-commits]

jmorse 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.

https://github.com/jmorse/llvm-project/commit/7b78ea87febc00b77ce8000659f61288c531eb09 <--- based on 
11a5026 with the addition of some x86 traps, which should cause tests covering those paths to fail.

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