[gold commit] Restore support for dwp v2 DWARF package file format

[Cary Coutant]

Back in August, I reverted the support for the dwp v2 format because
support for it wasn't yet in GDB. That support was added to GDB on
Oct. 4 (thanks, Doug!), so I'm now restoring the patch that switched
to the v2 format.

-cary


gold/
        * dwarf_reader.cc (Dwarf_info_reader::visit_type_unit): Add
        tu_length parameter.  Adjust all callers.
        * dwarf_reader.h (Dwarf_info_reader::visit_type_unit): Likewise.
        * dwp.cc: Include dwarf.h.
        (Section_bounds): New struct type.
        (Unit_set): New struct type.
        (Dwo_file::Dwo_file): Initialize new data member.
        (Dwo_file::read_compunit_index, Dwo_file::read_typeunit_index):
        Combine and rename to...
        (Dwo_file::read_unit_index): ...this.
        (Dwo_file::sized_read_compunit_index)
        (Dwo_file::sized_read_typeunit_index): Combine and rename to...
        (Dwo_file::sized_read_unit_index): ...this.
        (Dwo_file::copy_section): Remove section_name, is_str_offsets
        parameters; add section_id parameter.
        (Dwo_file::add_cu_set, Dwo_file::add_tu_set): Combine and rename to...
        (Dwo_file::add_unit_set): ...this.
        (Dwo_file::shndx_map_): Remove.
        (Dwo_file::sect_offsets_): New data member.
        (Dwp_output_file::Dwp_output_file): Initialize new data members.
        (Dwp_output_file::add_section): Rename to...
        (Dwp_output_file::add_contribution): ...this.
        (Dwp_output_file::add_cu_set): Combine parameters into a struct.
        (Dwp_output_file::add_tu_set): Likewise.
        (Dwp_output_file::Contribution): New type.
        (Dwp_output_file::Section::contributions): New data member.
        (Dwp_output_file::Cu_or_tu_set): Remove.
        (Dwp_output_file::Section::Section): New ctor.
        (Dwp_output_file::Dwp_index::Shndx_pool): Remove.
        (Dwp_output_file::Dwp_index::Section_table): New type.
        (Dwp_output_file::Dwp_index::Dwp_index): Initialize new data members.
        (Dwp_output_file::Dwp_index::enter_set): Change type of "set"
        parameter.
        (Dwp_output_file::Dwp_index::shndx_pool): Remove.
        (Dwp_output_file::Dwp_index::shndx_pool_end): Remove.
        (Dwp_output_file::Dwp_index::section_table): New member function.
        (Dwp_output_file::Dwp_index::section_table_end): New member function.
        (Dwp_output_file::Dwp_index::shndx_pool_size): Remove.
        (Dwp_output_file::Dwp_index::section_table_rows): New member function.
        (Dwp_output_file::Dwp_index::section_table_cols): New member function.
        (Dwp_output_file::Dwp_index::shndx_pool_): Remove.
        (Dwp_output_file::Dwp_index::section_table_): New data member.
        (Dwp_output_file::Dwp_index::section_mask_): New data member.
        (Dwp_output_file::add_output_section): New member function.
        (Dwp_output_file::write_new_section): New member function.
        (Dwp_output_file::write_contributions): New member function.
        (Dwp_output_file::section_id_map_): New data member.
        (class Dwo_id_info_reader): Remove.
        (class Unit_reader): New class.
        (get_dwarf_section_name): New function.
        (Dwo_file::read_executable): Adjust initializations of class data.
        (Dwo_file::read): Add support for v2 package file format.
        (Dwo_file::read_unit_index): Likewise.
        (Dwo_file::sized_read_unit_index): Likewise.
        (Dwo_file::copy_section): Likewise.
        (Dwo_file::add_unit_set): Likewise.
        (Dwp_output_file::add_output_section): Likewise.
        (Dwp_output_file::add_contribution): Likewise.
        (Dwp_output_file::Dwp_index::find_or_add): Use row index to check
        for empty slot.
        (Dwp_output_file::Dwp_index::enter_set): Add support for v2 package
        file format.
        (Dwp_output_file::Dwp_index::grow): Use row index to check for empty
        slot.
        (Dwp_output_file::initialize): Remove unused function.
        (Dwp_output_file::finalize): Add support for v2 package file format.
        (Dwp_output_file::write_index): Likewise.
        * gdb-index.cc (Gdb_index_info_reader::visit_type_unit): Adjust
        function prototype.