[llvm] [llvm] Fix __builtin_object_size interaction between Negative Offset … (PR #111827)

[Harald van Dijk via llvm-commits]

hvdijk wrote:

If I apply this PR locally, although I no longer see the UBSan error, I still get a number of differences in `__builtin_object_size` between Clang and GCC when I change my test to print `__builtin_object_size`'s result directly. I am not sure what the status of `__builtin_object_size` in Clang is, are we meant to return the same results as GCC?

https://github.com/llvm/llvm-project/pull/111827