[llvm] [SimplifyCFG][PGO] Reuse existing `setBranchWeights` (PR #160629)

[Mircea Trofin via llvm-commits]

mtrofin wrote:

### Merge activity

* **Oct 1, 4:52 PM UTC**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/160629).


https://github.com/llvm/llvm-project/pull/160629