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

[Vladislav Khmelevsky via llvm-commits]

yota9 wrote:

@maksfb Thanks for review, done. Please approve the patch. 

> My concern was that there could be a jump table with unused entries that were in unreachable code. 

I don't think this is the case here. We're optimising here BF with single-entry jump table the target of which we know.  I think we do optimise functions with jump tables, so it probably should be fine. Maybe I miss something though.. 

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