[llvm] [FunctionAttrs] deduce attr `cold` on functions if all CG paths call a `cold` function (PR #101298)

[via llvm-commits]

goldsteinn wrote:

> Okay, this has a notable negative impact on LTO compile times. Will try to fix.

Looked a bit, it seems like the compile time on LTO is all from LTO using the added `cold` attrs, not the time spent in `FunctionAttrs`.

Is this potentially acceptable?

https://github.com/llvm/llvm-project/pull/101298