[compiler-rt] [TySan] Fix false positives with derived classes (PR #126260)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

> Fixes issue https://github.com/llvm/llvm-project/issues/125079 as well as another case I discovered while trying to build LLVM with TySan.
The case when the access has an offset needs some slightly different legwork to the average check.

It would be great if you could spell out the differences, and ideally also make this clear in the code comments. 

https://github.com/llvm/llvm-project/pull/126260