[clang] [Clang] Fix missing diagnostic for non-standard layout type in `offsetof` (PR #65246)

[Takuya Shimizu via cfe-commits]

hazohelet wrote:

Adding an irrelevant new line in a modified test file would suffice to trigger the CI build.
Force-pushing doesn't seem to be desirable during code review.

https://github.com/llvm/llvm-project/pull/65246