[llvm] [BOLT][BTI] Refactor: move applyBTIFixup under MCPlusBuilder (PR #177164)

[Alexey Moksyakov via llvm-commits]

yavtuk wrote:

Do you mean the not all plt function should be patch? Only those which have patched callsite? What if we have 2 callsite with printf calls, func foo simple and callsite can be patch, func bar is not simple and call site can't be patch. Should we patch plt entry? Or we must create the duplicate plt entry without bti instruction

https://github.com/llvm/llvm-project/pull/177164