add_signal_thread_list.
* thread_pthread.c (unregister_ubf_list): renamed
  from remove_signal_thread_list.
* thread_pthread.c (ubf_wakeup_all_threads): renamed from
  ping_signal_thread_list.
* thread_pthread.c (ubf_wakeup_thread): renamed from
  ubf_select_each.
* thread_pthread.c (ubf_threads_empty): renamed from
  check_signal_thread_list().
* thread_pthread.c (ubf_list_lock): renamed from
  signal_thread_list_lock.

* thread_pthread.c (register_ubf_list): large simplification
  by using ccan/list.h.
  bonus: removed malloc() and exit(EXIT_FAILURE).
* thread_pthread.c (unregister_ubf_list): ditto.
* thread_pthread.c (ubf_threads_empty): ditto.
* thread_pthread.c (ubf_wakeup_all_threads): ditto.

* thread_pthread.c (print_signal_list): removed.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@52818 b2dd03c8-39d4-4d8f-98ff-823fe69b080e