[llvm] [LoopUnroll] Remove redundant debug instructions after blocks have been merged (PR #91246)

[via llvm-commits]

coderchenlin wrote:

@fhahn, Apologies for your time,  Could you help me to review this change again?  As @slackito found,  the original solution will introduce quadratic behavior in SimplifyCFG and make compilation time increase. Thus, I change the location, and put  the changes in loop-unrolling, and it won't have any effects in SimplifyCFG.  


https://github.com/llvm/llvm-project/pull/91246