Readelf: Add --lto-syms option to display LTO symbol tables.

Readelf: Add --lto-syms option to display LTO symbol tables.

	* readelf.c (do_lto_syms): New local.
	(long_option_values): Add OPTION_LTO_SYMS.
	(options): Add --lto-syms.
	(usage): Mention the new option.
	(parse_args): Parse the new option.
	(get_lto_kind): New function.
	(get_lto_visibility): New function.
	(get_lto_sym_type): New function.
	(display_lto_symtab): New function - displays the contents of an
	LTo symbol table section.
	(process_lto_symbol_tables): New functions.  Calls
	dipslay_lto_symtab on any LTO symbol table section.
	(process_object_file): Call process_lto_symbol_tables.
	* doc/binutils.texi: Document the new option.
	* NEWS: Mention the new feature.