[clang] [clang] Predefine `_CRT_USE_BUILTIN_OFFSETOF` in MS-compatible modes (PR #127568)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman approved this pull request.

LGTM! When landing, please add a release note to `clang/docs/ReleaseNotes.rst` so users know about the change.

https://github.com/llvm/llvm-project/pull/127568