[llvm] [LoopPeel] LCSSA form is destroyed by LoopPeel, preserve it (PR #78696)

[Manish Kausik H via llvm-commits]

Nirhar wrote:

@vedantparanjape-amd , going by the definition of LCSSA, I see that %0 is not used anywhere outside of the loop headed by bb1 except by the phi node in bb7, which I believe is permitted(going by this example in llvm-docs [Link](https://llvm.org/docs/LoopTerminology.html#loop-closed-ssa-lcssa)). 

If that is the case, I believe that this test case hit some corner condition which was not considered by `isRecursivelyInLCSSAForm` and thus the patch must modify that. 

@nikic @vedantparanjape-amd Please correct me if I am wrong, I am trying to refine my understanding of LCSSA

https://github.com/llvm/llvm-project/pull/78696