Linker plugins should be aware of --defsym during symbol resolution

[Cary Coutant]

> Hmmm, in get_symbol_resolution_info, we have this:
>
>   if (nsyms > this->nsyms_)
>     return LDPS_NO_SYMS;
>
> That needs to be qualified with a test for version > 2 (as was done a
> few lines below).

Ignore this -- we always returned NO_SYMS in this case, but added the
new case just below with LDPT_GET_SYMBOLS_V3. Sorry!

-cary