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

[Nico Weber via cfe-commits]

nico wrote:

Will it land very soon? If so, happy to let it land and see what our bots say.

(If not, https://llvm.org/docs/DeveloperPolicy.html#patch-reversion-policy)

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