In C++20, a defaulted but implicitly deleted destructor is constexpr if
and only if the class has no virtual base class. This hasn't been
changed in C++23 by P2448R2.
Constexpr-ness on a deleted destructor affects almost nothing. The
`__is_literal` intrinsic is related, while the corresponding
`std::is_literal_type(_v)` utility has been removed in C++20. A recently
added example in `test/AST/ByteCode/cxx23.cpp` will become valid, and
the example is already accepted by GCC.
Clang currently behaves correctly in C++23 mode, because the
constexpr-ness on defaulted destructor is relaxed by P2448R2. But we
should make similar relaxation for an implicitly deleted destructor.
Fixes#85550.
