thread.c: ptid_equal -> operator==

thread.c: ptid_equal -> operator==

gdb/ChangeLog:
2017-04-10  Pedro Alves  <palves@redhat.com>

	* thread.c (add_thread_silent, delete_thread_1, find_thread_ptid)
	(ptid_to_global_thread_id, in_thread_list)
	(do_captured_list_thread_ids, set_resumed, set_running)
	(set_executing, set_stop_requested, finish_thread_state)
	(validate_registers_access, can_access_registers_ptid)
	(print_thread_info_1, switch_to_thread)
	(do_restore_current_thread_cleanup)
	(make_cleanup_restore_current_thread, thread_command)
	(thread_name_command): Use operator== instead of ptid_equal.