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

[Alexander Richardson via cfe-commits]

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arichardson wrote:

Fair point, maybe something like `CreateElemCountPtrDiff`. But no need to include that in this pull request.

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