Code reorg in preparation for adding comdat types support.

	Code reorg in preparation for adding comdat types support.
	* dwarf2read.c (struct die_reader_specs): New struct.
	(locate_pdi_sibling): New arg buffer.  All callers updated.
	(load_partial_dies, read_partial_die): Ditto.
	(read_8_bytes): Change return type to ULONGEST.
	(read_comp_unit): Delete arg abfd.  All callers updated.
	(read_die_and_children_1): Delete args abfd, cu.  New arg reader.
	All callers updated.
	(read_die_and_children, read_die_and_siblings): Ditto.
	(read_full_die): Ditto.  Move closer to callers.
	(skip_one_die): New arg buffer.  All callers updated.
	(load_full_comp_unit): Change return type to void.  All callers
	updated.
	(partial_read_comp_unit_head): New args buffer, buffer_size.
	All callers updated.
	(process_psymtab_comp_unit): New function, split out from
	dwarf2_build_psymtabs_hard.
	(dwarf2_build_psymtabs_hard): Call it.
	(load_partial_comp_unit): Renamed from load_comp_unit.
	All callers updated.
	(skip_children): New arg buffer.  All callers updated.
	(init_cu_die_reader): New function.
	(is_ref_attr): New function.
	(dwarf2_get_ref_die_offset): Call it.
	(alloc_one_comp_unit): New function.