[llvm] [InstCombine] Support multi-use values in cast elimination transforms (PR #165877)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

Compile-time impact looks neutral: https://llvm-compile-time-tracker.com/compare.php?from=77342761a9060159f09c0c6d5aa3da2e543a4877&to=eb3f87eb97f6e93b33c4e1bec33bb8d2eab3903c&stat=instructions:u

https://github.com/llvm/llvm-project/pull/165877