[llvm] [ReachingDefAnalysis] Fix management of MBBFrameObjsReachingDefs (PR #124943)

[Mikhail Gudim via llvm-commits]

mgudim wrote:

Since there is nothing using this in llvm right now these changes shouldn't break anything.
We can either:
(1) merge this and hope it's all good.
(2) I can rebase my shrink-wrapping patch on top of this and I can run all of spec - that should be a good test.

What do you think @michaelmaitland ?

https://github.com/llvm/llvm-project/pull/124943