[llvm] [HotColdSplit] Add `nofuncsplit` attribute and skip it in HotColdSplit pass (PR #179002)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

I found that we have an existing `"nooutline"` attribute. I think we should use it here instead of introducing a new one, as hot cold splitting is effectively a form of outlining.

https://github.com/llvm/llvm-project/pull/179002