[Issue 23189] importC: __builtin_offsetof without struct/union/enum doesn't compile

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23189

--- Comment #3 from ryuukk_ <ryuukk.dev at gmail.com> ---
Ok apparently, it is required to have them, but that was the output of the
clang preprocessor.. hmm

Anyways.. i think a proper error message would be more useful that what is
currently emitted!

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