[llvm] [LSR] Change the computing method of Cost.ImmCost and rewrite equality icmp (PR #96044)

[Zhijin Zeng via llvm-commits]

zengdage wrote:

I think the two pr should be reviewed together. https://github.com/llvm/llvm-project/pull/96048. After the two pr, it can reduce dynamic instruction counts for function __find_if in stl_algobase.h

https://github.com/llvm/llvm-project/pull/96044