[clang] Rewrite offsetof with __builtin_offsetof with -fms-kernel (PR #193804)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

> Can you share a godbolt link showing what you mean? 

https://godbolt.org/z/3688PTeG1 .

https://github.com/llvm/llvm-project/pull/193804