Add support for skeletonless type units.

Add support for skeletonless type units.

	* dwarf2read.c (struct dwarf2_per_objfile): New member
	n_allocated_type_units.
	(struct dwarf2_per_objfile) <tu_stats>: New member
	nr_all_type_units_reallocs.
	(create_signatured_type_table_from_index): Initialize
	n_allocated_type_units
	(create_all_type_units): Ditto.
	(add_type_unit): Move up in file.  New arg slot.
	All callers updated.  Increase space for all_type_units more
	efficiently.
	(fill_in_sig_entry_from_dwo_entry): Handle psymtabs.
	(lookup_dwo_signatured_type): Handle skeletonless TUs.
	(lookup_dwp_signatured_type): Ditto.
	(init_tu_and_read_dwo_dies): New arg use_existing_cu.
	All callers updated.
	(build_type_psymtabs_1): Leave type_unit_groups as
	NULL if no TUs present.
	(print_tu_stats): New function.
	(process_skeletonless_type_unit): New function.
	(process_dwo_file_for_skeletonless_type_units): New
	function.
	(process_skeletonless_type_units): New function.
	(dwarf2_build_psymtabs_hard): Handle skeletonless TUs.
	Call print tu_stats if debugging enabled.