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

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> My biggest concern that this is introducing an incompatibility with MSVC; this is not how MSVC handles these constructs.

Can you share a godbolt link showing what you mean? I did some simple testing and it does seem to be defined behavior in MSVC: https://godbolt.org/z/v5nsjYqvr

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