[clang] [CIR] Combined virtual + non-virtual base offset (PR #192617)

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xiongzile wrote:

Hi @andykaylor 
Apologies for the delay — I’ve been tied up with work recently.
I updated the test, but noticed that the LLVM IR generated via ``-fclangir`` differs from the default pipeline. These differences appear to be unrelated to my changes, so I’ve left them as-is instead of trying to unify the outputs.
Core difference I guess is the null check. ``-fclangir`` might not do the null check. 

https://github.com/llvm/llvm-project/pull/192617