gdbserver: make thread_info non-POD Add a constructor and a destructor. The constructor takes care of the initialization that happened in add_thread, while the destructor takes care of the freeing that happened in free_one_thread. This is needed to make target_waitstatus non-POD, as thread_info contains a member of that type. Change-Id: I1db321b4de9dd233ede0d5c101950f1d6f1d13b7