Extend readelf and objdump so that they will display and follow multiple links to...

Extend readelf and objdump so that they will display and follow multiple links to separate debug information files.

	PR 23843
	* dwarf.h (struct separate_info): New structure for containing
	information on separate debug info files.
	* dwarf.c (struct dwo_info): New structure for containing dwo
	links.
	(first_dwo_info): Chain of dwo_info structures.
	(first_separate_file): Chain of separate_info structures.
	(separate_debug_file, separate_debug_filename): Delete.
	(fetch_alt_indirect_string): Scan all separate debug info files
	for the requested string.
	(add_dwo_info): New function.
	(add_dwo_name): New function.
	(add_dwo_dir): New function.
	(add_dwo_id: New function.
	(free_dwo_info): New function.
	(read_and_display_attr_value): Store DWO data using the new
	functions.
	(load_debug_section_with_follow): If necessary, scan the list of
	separate debug info files for the requested section.
	(add_separate_debug_file): New function.
	(load_separate_debug_info): Call add_separate_debug_file to store
	the information on the newly loaded file.
	(load_dwo_file): Likewise.
	(load_separate_debif_file): Rename to load_separate_debug_files.
	Change return type to boolean.  If following links then attempt to
	load all separate debug info files, not just the first one.
	(free_debug_memory): Release memory in dwo_info and separate_info
	chains.
	* objdump.c (dump_dwarf): Iterate over all loaded debg info files.
	* readelf.c (process_object): Likewise.
	* doc/debug.options.texi: Update descriptions of links and
	follow-links options.
	* testsuite/binutils-all/objdump.WK2: Update expected output.
	* testsuite/binutils-all/readelf.k2: Likewise.
	* NEWS: Announce the new feature.