[llvm] IR: Simplify BlockAddress replacement (PR #135360)

[Matt Arsenault via llvm-commits]

arsenm wrote:

### Merge activity

* **Apr 11, 11:00 AM EDT**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/135360).


https://github.com/llvm/llvm-project/pull/135360