[llvm] [BOLT] Enhance fixed indirect branch handling (PR #71324)

[Maksim Panchenko via llvm-commits]

maksfb wrote:

> @maksfb Fill free to write me if you need a help with difference analyses :)

The miscompare was nothing serious and everything else passes. My concern was that there could be a jump table with unused entries that were in unreachable code. Since we ignore the jump table and optimize the function with UCE, we could end-up with the jump table referencing undefined labels. But I couldn't find any binary with such an anomaly. Even if this happens, we can implement a better protection mechanism against undefined symbols.

TL;DR: LGTM except for POSSIBLE_GOTO change. Please update the summary too.

https://github.com/llvm/llvm-project/pull/71324