[llvm] [InstCombine] Mark as unknown the branch weights of packed integer selecting shifts (PR #162726)

[Mircea Trofin via llvm-commits]

mtrofin wrote:

### Merge activity

* **Oct 10, 5:28 PM UTC**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/162726).


https://github.com/llvm/llvm-project/pull/162726