[clang] [Clang][CodeGen] Use ptrtoaddr for pointer diff (PR #210729)

[Alexis Engelke via cfe-commits]

aengelke wrote:

[c-t-t size-text](https://llvm-compile-time-tracker.com/compare.php?from=743813d10023a0616833062f5d448284022b8063&to=e94ccc5d21931cd24b0846b7df33596ec221752a&stat=size-text) shows differences up to +0.2% for tramp3d-v4 -O3. Not sure what a good way to evaluate the impact is, it looks like llvm-opt-benchmark starts from bitcode files.

https://github.com/llvm/llvm-project/pull/210729