[Bug c++/91159] Compilation error on explicitly defaulting default constructor of an abstract class with virtual base class

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91159

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Ah, this is https://wg21.link/cwg1611 and was fixed by
https://wg21.link/cwg1658