Stop readekf and objdump from aggressively following links.

Stop readekf and objdump from aggressively following links.

	* dwarf.c (dwarf_select_sections_by_names): Return zero if no
	sections were selected.
	(dwarf_select_sections_by_letters): Likewise.
	* dwarf.h: (dwarf_select_sections_by_names): Update prototype.
	(dwarf_select_sections_by_letters): Update prototype.
	* objdump.c (might_need_separate_debug_info): New function.
	(dump_bfd): Call new function before attempting to load separate
	debug info files.
	(main): Do not enable dwarf section dumping for -WK or -WN.
	* readelf.c (parse_args): Do not enable dwarf section dumping for
	-wK or -wN.
	(might_need_separate_debug_info): New function.
	(process_object): Call new function before attempting to load
	separate debug info files.
	* testsuite/binutils-all/debuginfo.exp: Expect -WE and -wE
	debuginfod tests to pass.
	* testsuite/binutils-all/objdump.Wk: Add extra regexps.
	* testsuite/binutils-all/readelf.k: Add extra regexps.