[clang] [LifetimeSafety] Avoid adding already present items in sets/maps (PR #159582)

[Utkarsh Saxena via cfe-commits]

usx95 wrote:

### Merge activity

* **Sep 19, 3:59 PM UTC**: [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/159582) rebased this pull request as part of a merge.


https://github.com/llvm/llvm-project/pull/159582