[PATCH][gold] Mips: Omit empty objects for merging processor-specific data

[Cary Coutant]

>         * mips.cc (Mips_relobj::merge_processor_specific_data_): New data
>         member.
>         (Mips_relobj::merge_processor_specific_data): New method.
>         (Mips_relobj::do_read_symbols): Set merge_processor_specific_data_
>         to false, only if the input file is a binary or if object has no
>         contents except the section name string table and an empty symbol
>         table with the undefined symbol.
>         (Target_mips::do_finalize_sections): Refactor.  Skip empty object files
>         for merging processor-specific data.

Committed on your behalf.

-cary