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

[manu at gcc dot gnu.org]

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

--- Comment #24 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
For completeness, this is what LLD says:

ld.lld: error: undefined symbol: vtable for A
>>> referenced by example.cpp:7
>>>               /tmp/example-5d8b98.o:(A::A())
>>> the vtable symbol may be undefined because the class is missing its key function (see https://lld.llvm.org/missingkeyfunction)

which seems better.