[llvm] [BOLT] Impute missing trace fall-through (PR #145258)

[Maksim Panchenko via llvm-commits]

maksfb wrote:

Nice results. How does that approach compare to dropping a trace corresponding to the TOS entry, and only using the TOS branch source for establishing the fall-though end for a previous trace?

https://github.com/llvm/llvm-project/pull/145258