Add DWARF 5 support in gold.

elfcpp/
	PR gold/27246
	* dwarf.h (enum DW_LNCT): Add line number table content type codes.
	(enum DW_LINE_OPS): Reformat.
	(enum DW_LINE_EXTENDED_OPS): Reformat.
	(enum DW_CHILDREN): Reformat.
	(enum DW_RLE): Add range list entry types.
	(enum DW_SECT): Update values for DWARF 5.

gold/
	PR gold/27246
	* dwarf_reader.cc (Dwarf_abbrev_table::do_get_abbrev): Handle
	DW_FORM_implicit_const.
	(Dwarf_ranges_table::read_ranges_table): Add version parameter;
	Adjust all callers.  Look for .debug_rnglists section if DWARF 5.
	(Dwarf_ranges_table::read_range_list_v5): New method.
	(Dwarf_die::read_attributes): Handle new DWARF 5 DW_FORM codes.
	(Dwarf_die::skip_attributes): Likewise.
	(Dwarf_info_reader::do_parse): Support DWARF 5 unit header format.
	(Dwarf_info_reader::read_3bytes_from_pointer): New method.
	(Sized_dwarf_line_info::Sized_dwarf_line_info): Initialize
	str_buffer_, str_buffer_start, reloc_map_, line_number_map_.
	Look for .debug_line_str section.
	(Sized_dwarf_line_info::read_header_prolog): Support DWARF 5 prolog.
	(Sized_dwarf_line_info::read_header_tables): Rename to...
	(Sized_dwarf_line_info::read_header_tables_v2): ... this.
	(Sized_dwarf_line_info::read_header_tables_v5): New method.
	(Sized_dwarf_line_info::process_one_opcode): Insert missing "this->".
	Change advance_line to signed int64_t.
	(Sized_dwarf_line_info::read_lines): Add endptr parameter; adjust
	callers.  Insert missing "this->".
	(Sized_dwarf_line_info::read_line_mappings): Support DWARF 5.
	(Sized_dwarf_line_info::do_addr2line): Add debug code.
	* dwarf_reader.h (Dwarf_abbrev_table::Attribute): Add implicit_const
	field. Adjust constructor.
	(Dwarf_abbrev_table::add_sttribute): Add implicit_const parameter.
	(Dwarf_ranges_table::read_ranges_table): Add version parameter.
	(Dwarf_ranges_table::read_range_list_v5): New method.
	(Dwarf_die): Remove unused attr_off field.
	(Dwarf_info_reader::Dwarf_info_reader): Initialize unit_type_ field.
	(Dwarf_info_reader::is_type_unit): New method.
	(Dwarf_info_reader::read_3bytes_from_pointer): New method.
	(Dwarf_info_reader::read_range_list): Call read_range_list_v5 for
	DWARF 5 range lists.
	(Dwarf_info_reader::is_type_unit_): Remove.
	(Dwarf_info_reader::unit_type_): New field.
	(Sized_dwarf_line_info::~Sized_dwarf_line_info): Delete
	str_buffer_start_.
	(Sized_dwarf_line_info::read_header_tables): Rename to...
	(Sized_dwarf_line_info::read_header_tables_v2): ... this.
	(Sized_dwarf_line_info::read_header_tables_v5): New method.
	(Sized_dwarf_line_info::read_lines): Add endptr parameter.
	(Sized_dwarf_line_info::Dwarf_line_infoHeader): Add address_size field.
	(Sized_dwarf_line_info::str_buffer_): New field.
	(Sized_dwarf_line_info::str_buffer_end_): New field.
	(Sized_dwarf_line_info::str_buffer_start_): New field.
	(Sized_dwarf_line_info::end_of_header_length_): New field.
	(Sized_dwarf_line_info::end_of_unit_): New field.