* incremental-dump.cc (dump_incremental_inputs): Print COMDAT groups.

	* incremental-dump.cc (dump_incremental_inputs): Print COMDAT groups.
	* incremental.cc (Incremental_inputs::report_input_section): Fix
	comment, indentation.
	(Incremental_inputs::report_comdat_group): New function.
	(Output_section_incremental_inputs::set_final_data_size): Adjust size
	of data for incremental input file entry.
	(Output_section_incremental_inputs::write_info_blocks): Write COMDAT
	group count, COMDAT group signatures.
	(Sized_incr_relobj::do_layout): Record kept COMDAT group info from
	an unchanged input file.
	* incremental.h (Incremental_object_entry::Incremental_object_entry):
	Initialize new data member.
	(Incremental_object_entry::add_comdat_group): New function.
	(Incremental_object_entry::get_comdat_group_count): New function.
	(Incremental_object_entry::get_comdat_signature_key): New function.
	(Incremental_object_entry::groups_): New data member.
	(Incremental_inputs::report_comdat_group): New function.
	(Incremental_input_entry_reader::get_symbol_offset): Adjust size of
	data for incremental input file entry.
	(Incremental_input_entry_reader::get_comdat_group_count): New function.
	(Incremental_input_entry_reader::get_input_section): Adjust size of
	data for incremental input file entry.
	(Incremental_input_entry_reader::get_global_symbol_reader): Likewise.
	(Incremental_input_entry_reader::get_comdat_group_signature): New
	function.
	* object.cc (Sized_relobj::include_section_group): Report kept
	COMDAT groups for incremental links.