Add support for comdat type sections for DWARF v4.

Add support for comdat type sections for DWARF v4.

	Add support for comdat type sections for DWARF v4.  Merge from dwarf4
	branch.
	* dwarf2out.c (DWARF_TYPE_SIGNATURE_SIZE): New constant.
	(dw_die_ref): Define vector type.
	(enum dw_val_class): Add dw_val_class_data8.
	(struct dw_val_struct): Add v.val_data8.
	(comdat_type_node_ref): New type.
	(struct die_struct): Move die_symbol into a union; add new field
	die_type_node.  Change all uses.
	(comdat_type_node): New type.
	(skeleton_chain_node): New type.
	(DWARF_COMDAT_TYPE_UNIT_HEADER_SIZE): New constant.
	(comdat_type_list): New variable.
	(dwarf_tag_name): Add DW_TAG_type_unit.
	(dwarf_attr_name): Add DW_AT_signature.
	(add_AT_data8): New function.
	(replace_child): New function.
	(move_all_children): New function.
	(print_signature): New function.
	(print_die): Print signature information; add dw_val_class_data8.
	(attr_checksum): Support dw_val_class_data8.
	(CHECKSUM_STRING): Redefine for DWARF-4 to include
	trailing NULL byte.
	(CHECKSUM_SLEB128, CHECKSUM_ULEB128): New macros.
	(checksum_sleb128, checksum_uleb128): New functions.
	(checksum_die_context): New function.
	(loc_checksum_ordered): New function.
	(attr_checksum_ordered): New function.
	(struct checksum_attributes): New structure.
	(collect_checksum_attributes): New function.
	(die_checksum_ordered): New function.
	(generate_type_signature): New function.
	(same_dw_val_p): Add dw_val_class_data8.
	(is_symbol_die): Use new is_declaration_die function.
	(is_declaration_die): New function.
	(should_move_die_to_comdat): New function.
	(clone_die): New function.
	(clone_tree): New function.
	(clone_as_declaration): New function.
	(copy_declaration_context): New function.
	(generate_skeleton_ancestor_tree): New function.
	(generate_skeleton_bottom_up): New function.
	(generate_skeleton): New function.
	(remove_child_or_replace_with_skeleton): New function.
	(break_out_comdat_types): New function.
	(struct decl_table_entry): New type.
	(htab_decl_hash): New function.
	(htab_decl_eq): New function.
	(htab_decl_del): New function.
	(copy_ancestor_tree): New function.
	(copy_decls_walk): New function.
	(copy_decls_for_unworthy_types): New function.
	(build_abbrev_table): Don't assert on missing die_symbol when doing
	comdat type sections.
	(size_of_die): Use DW_FORM_sig8 for external references; Add
	dw_val_class_data8.
	(unmark_dies): Don't assert for unmarked dies when doing comdat
	type sections.
	(value_format): Support DW_FORM_sig8 and dw_val_class_data8.
	(output_signature): New function.
	(output_die): Likewise.
	(output_compilation_unit_header): Mark output as DWARF version 3
	even if generating DWARF 4.
	(output_comdat_type_unit): New function.
	(output_line_info): Mark output as DWARF version 3 even if generating
	DWARF 4.
	(dwarf2out_start_source_file): Don't do eliminate_dwarf2_dups with
	DWARF-4.
	(dwarf2out_end_source_file): Likewise.
	(prune_unused_types_walk_attribs): Don't follow references into
	comdat type sections.
	(prune_unused_types_mark): When generating type units, do not mark
	children of non-defining declarations of types; do mark children of
	type entries.
	(prune_unused_types): Process comdat type sections.
	(htab_ct_hash): New function.
	(htab_ct_eq): New function.
	(dwarf2out_finish): Move types to comdat sections when using DWARF-4.
	Add a pointer to the line table from type unit entries so
	DW_AT_decl_file has meaning.
	* varasm.c (default_elf_asm_named_section): Use identifier name as
	comdat key instead of lang hook.

From-SVN: r152421