[PATCH] gold: remove unused methods in Output_data_got_powerpc

[Cary Coutant]

> Another option, avoiding the need for a virtual function and the
> overhead this adds for all targets, is to override add_global(),
> add_global_plt() etc. in Output_data_got_powerpc.  This keeps the
> overhead to powerpc.cc.  Is this preferable?
>
> I also moved add_constant_pair into output.h for symmetry (and just in
> case someone decided to optimise addition of constants).

This looks good to me. Thanks!

-cary