[GOLD] Reduce size of class Symbol

[Cary Coutant]

>         * symtab.h (Symbol): Split u_ into u1_ and u2_.  Move plt_offset_
>         before got_offsets_.  Adjust accessors to suit.
>         * symtab.cc (Symbol::init_fields): Adjust for union change.
>         (Symbol::init_base_output_data): Likewise.
>         (Symbol::init_base_output_segment): Likewise.
>         (Symbol::allocate_base_common): Likewise.
>         (Symbol::output_section): Likewise.
>         (Symbol::set_output_section): Likewise.
>         (Symbol::set_output_segment): Likewise.
>         * resolve.cc (Symbol::override_base): Likewise.
>         (Symbol::override_base_with_special): Likewise.

This is OK. Thanks!

-cary