[clang] [llvm] [llvm][fatlto] Add FatLTOCleanup pass (PR #125911)

[Paul Kirth via cfe-commits]

ilovepi wrote:

### Merge activity

* **Feb 13, 2:38 PM EST**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/125911).


https://github.com/llvm/llvm-project/pull/125911