BFD library: Use entry 0 in directory and filename tables of DWARF-5 debug info.

	PR 29529
	* dwarf2.c (struct line_info_table): Add new field:
	use_dir_and_file_0.
	(concat_filename): Use new field to help select the correct table
	slot.
	(read_formatted_entries): Do not skip entry 0.
	(decode_line_info): Set new field depending upon the version of
	DWARF being parsed.  Initialise filename based upon the setting of
	the new field.