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

[Nico Weber via cfe-commits]

nico wrote:

Landing this, as #219156 didn't change anything (https://logs.chromium.org/logs/chromium/buildbucket/cr-buildbucket/8672305897337090897/+/u/package_clang/stdout?format=raw)

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