[llvm] [InstCombine] Fold `(op x, ({z,s}ext (icmp eq x, C)))` to select (PR #89020)

[via llvm-commits]

goldsteinn wrote:

Closing because we pushed: https://github.com/llvm/llvm-project/commit/0310f7f2d0c56a5697710251cec9803cbf7b4d56 to handle the `add` case

https://github.com/llvm/llvm-project/pull/89020