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

[Devon Loehr via cfe-commits]

DKLoehr wrote:

I tried earlier but github wasn't having it. I hacked the extension to .txt to work around it:

[ir_17801.txt](https://github.com/user-attachments/files/31486152/it_17801.txt)
[ir_17802.txt](https://github.com/user-attachments/files/31486155/it_17802.txt)


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