[clang] [llvm] [mlir] [IRBuilder] Use ptrtoaddr in CreatePtrDiff() (PR #181855)

[Alexander Richardson via llvm-commits]

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arichardson wrote:

Maybe now that we have two overloads, this one could be called `CreateCStylePtrDiff` to make it obvious that first argument is used for the element type?

https://github.com/llvm/llvm-project/pull/181855