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

[via cfe-commits]

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@@ -47,7 +47,13 @@ struct __libcpp_datasizeof {
   };
 #endif
 
+  // Disable warnings related to the use of `offsetof` on non-standard layout or non-POD types
+  // TODO : Find a way to replace `offsetof` ?
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philnik777 wrote:

I don't think this TODO is actionable from the libc++ side of things currently, so I'd rather not add it. `offsetof` is the right tool for what we are trying to achieve - even if it's technically UB.

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