Prior to P2448R2 we were more aggressive in diagnosing ill-formed constexpr functions. Many of these restrictions were relaxed and now it is not required for defaulted comparison operators to call constexpr functions.
This behavior is extended to before C++23 and diagnostic for it's use can be enabled w/ -pedantic or -Wc++2b-default-comp-relaxed-constexpr
This fixes: https://github.com/llvm/llvm-project/issues/61238
Should we also say what's still missing that causes this to be partial?