[llvm] Replace uses of ConstantExpr::getCompare. (PR #91558)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

Made suggested change. I didn't change the use in llvm/lib/IR/Constants.cpp; I think that would introduce a circular dependency.

Note that this is not NFC anymore; folding using the datalayout actually unblocks transforms in a few places.

https://github.com/llvm/llvm-project/pull/91558