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

[via llvm-commits]

goldsteinn wrote:

> LGTM
> 
> I looked at some cases where code size increases with this patch, and the effect is basically that we don't inline an error handling path, and that reduces the size of a function below the inlining threshold, so it gets inlined (a lot more) in turn. Overall effect is undesirable, but the decisions are all locally reasonable.

The stats had less total inlining w/ this patch.
```diff
-           27730 inline                       - Number of functions deleted because all callers found
-          106114 inline                       - Number of functions inlined
-          132759 inline-cost                  - Number of call sites analyzed
+           27703 inline                       - Number of functions deleted because all callers found
+          105963 inline                       - Number of functions inlined
+          132883 inline-cost                  - Number of call sites analyzed
```

Before I push this, Ill add a stat for total number of callsites inlined which AFAICT is: `IFI.InlinedCallSites.size()` as that is probably a useful metric.

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