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

[Abdulmalek Almkainzi via cfe-commits]

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aalmkainzi wrote:

should I try to make assigning compound literal with non-null pointer also error out if `-fexperimental-new-constant-interpreter`?

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