[clang] Revert "[Clang][CodeGen] Use ptrtoaddr for pointer diff (#210729)" (PR #219203)

[Wenju He via cfe-commits]

wenju-he wrote:

> I'd like a confirmation that #219156 does not resolve the issue before this gets reverted.

#219156 does not resolve two of our downstream regressions caused by #210729. I haven't identified the root cause yet, so it is still unclear whether this is an upstream or downstream bug.

https://github.com/llvm/llvm-project/pull/219203