[llvm] [CFI] Propagate GUIDs correctly after PR #184065 (PR #200542)

[Mircea Trofin via llvm-commits]

mtrofin wrote:

> > > Wait, that's also using GUID underneath.
> > 
> > 
> > We started using the GUID to optimize name lookups in #130382. The final lookup has always been based on the name. Using a different GUID for the initial lookup will likely break some invariants that `CfiFunctionIndex` depends on.
> 
> I see - so in this case it's basically an implementation detail, and, while hash collisions may still happen, placing this guid in the global namespace used by thinlto is undesirable, if I understand it correctly.

(looking more) it seems, however, that there is a current assumption about the GUID being the same as the one used by ThinLTO: see `BitcodeWriter.cpp:5368` - the use of `DefOrUseGUIDs`. @vitalybuka? (PR #130382)

https://github.com/llvm/llvm-project/pull/200542