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

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

Maybe MSVC has logic similar to `-Wgnu-folding-constant`?  clang also folds the array bounds in your example.

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