Provide string description of definition, visibility and resolution in LTO plug-in.
ld/ChangeLog:
2019-02-26 Martin Liska <mliska@suse.cz>
* plugin.c (get_symbols): Add lto_kind_str, lto_resolution_str,
lto_visibility_str and use then to inform about plugin-symbols.
* testsuite/ld-plugin/plugin-12.d: Adjust expected pattern.