[compiler-rt] [llvm] [ctxprof] Prepare profile format for flat profiles (PR #129626)

[Mircea Trofin via llvm-commits]

mtrofin wrote:

### Merge activity

* **Mar 5, 10:20 AM EST**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/129626).


https://github.com/llvm/llvm-project/pull/129626