[Bug other/42540] c++ error message [vtable undefined] is unhelpful

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=42540

--- Comment #22 from Jonathan Wakely <redi at gcc dot gnu.org> ---
https://itanium-cxx-abi.github.io/cxx-abi/abi.html#vague-vtable

The ABI specifies it