[gold patch] RFC: Add extra note when 'vtable for C' is undefined

[Cary Coutant]

>> Ian, I'm doing a simple check for "_ZTV" here -- for a bit of extra
>> portability, I could also demangle the symbol name into components and
>> look for DEMANGLE_COMPONENT_VTABLE, but it just didn't seem worth it.
>
> I agree.
>
>> Also, I could have put the check in gold_undefined_symbol_at_location,
>> or in Errors::undefined_symbol. Do you have any preference?
>
> I think that where you have it is fine, especially if you wind up
> making it smarter.

Thanks, I've committed it as is.

-cary