[llvm] [HCS] Externd to outline overlapping sub/super cold regions (PR #80732)

[Shimin Cui via llvm-commits]

scui-ibm wrote:

> Overall lgtm, please add comments as mentioned in the review. Thanks for working on this.

Thanks a lot for the quick review and approval. I'll add some comments to the code.

https://github.com/llvm/llvm-project/pull/80732