[clang] [Clang] Fix misleading diagnostic for pointer const type static data member (PR #223596)

[Corentin Jabot via cfe-commits]

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cor3ntin wrote:

In addition to that, suggesting constexpr in C++98 would be... rather confusing I think. So I'm not sure there is anything to fix here either.

https://github.com/llvm/llvm-project/pull/223596