[llvm] [IRBuilder] Add CreatePtrAdd() method (NFC) (PR #77582)

[Yingwei Zheng via llvm-commits]

https://github.com/dtcxzyw approved this pull request.

LGTM. Did you see any warnings about unused variables? Some `Int8Ty`s may be unused after this patch.


https://github.com/llvm/llvm-project/pull/77582