Add support for "comdat types" from DWARF4.

	Add support for "comdat types" from DWARF4.
	* dwarf2read.c (dwarf2_per_objfile): New member types,
	signatured_types.
	(TYPES_SECTION): New macro.
	(dwarf2_per_cu_data): Change size of length field from 30 bits
	to 29 bits.  New member from_debug_types.
	(signatured_type): New struct.
	(struct attribute): New union member signatured_type.
	(DW_SIGNATURED_TYPE): New macro.
	(dwarf2_attr_no_follow): New function.
	(read_type_unit_scope): New function.
	(follow_die_ref_or_sig, follow_die_sig): New functions.
	(dwarf2_locate_sectoins): Handle .debug_types.
	(dwarf2_build_psymtabs): Read .debug_types.
	(read_type_comp_unit_head): New function.
	(hash_type_signature, eq_type_signature): New functions.
	(create_debug_types_hash_table): New function.
	(lookup_signatured_type): New function.
	(process_psymtab_comp_unit): Handle type units too.
	(process_type_comp_unit, build_type_psymtabs): New functions.
	(dwarf2_build_psymtabs_hard): Call build_type_psymtabs.
	(load_partial_comp_unit): Assert not called for a type unit.
	(skip_one_die): Handle DW_FORM_sig8.
	(queue_comp_unit): Don't call load_full_comp_unit here, or
	update read_in_chain.
	(psymtab_to_symtab_1): Call read_signatured_type_at_offset for
	type units, or load_full_comp_unit for comp units after
	queue_comp_unit returns.
	(load_full_comp_unit): Assert not called for type units.
	(load_full_comp_unit): Update read_in_chain here.
	(process_die): Handle DW_TAG_type_unit.
	(read_structure_type): Look for signatured types.
	(read_enumeration_type): Ditto.
	(init_cu_die_reader): Handle .debug_types.
	(read_comp_unit): Assert hash not computed yet.
	(read_die_and_children): Expand debugging printf to handle .debug_types.
	(read_partial_die): Handle DW_TAG_type_unit:
	(find_patial_die): Handle .debug_types.
	(read_attribute_value): Handle DW_FORM_sig8.
	(die_type): Call follow_die_ref_or_sig instead of follow_die_ref.
	(die_containing_type): Ditto.
	(dwarf_tag_name): Handle DW_TAG_type_unit.
	(dwarf_attr_name): Handle DW_AT_signature.
	(dwarf_form_name): Handle DW_FORM_sec_offset, DW_FORM_exprloc,
	DW_FORM_flag_present, DW_FORM_sig8.
	(dump_die_shallow): Handlel DW_FORM_sig8.
	(maybe_queue_comp_unit): Change return type to int from void.
	All callers updated.
	(follow_die_ref): Handle .debug_types.
	(lookup_signatured_type_at_offset): New function.
	(read_signatured_type_at_offset): New function.
	(read_signatured_type): New function.