gdb: pass info_threads_opts to print_thread_info_1

The "info threads" command tracks its options in a struct named
'info_threads_opts', which currently has only one option.  Pass the
whole options object to helper functions, instead of passing
the option value individually.  This is a refactoring to make adding
more options easier.

Reviewed-By: Guinevere Larsen <guinevere@redhat.com>
Approved-by: Pedro Alves <pedro@palves.net