[clang] [clang] Reject initializing constexpr struct/union types with compound literals that contain non null pointers (PR #228776)

[Yanzuo Liu via cfe-commits]

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zwuis wrote:

Should not be in `Parser`. Perhaps we can put it in `Sema` but I don't know if there is a better place.

Try to add tests to a pre-existing file.

https://github.com/llvm/llvm-project/pull/228776