rem: return thread->sig_pending & ~thread->sig_block_mask;
add: return atomic_get(&thread->sig_pending) & ~atomic_get(&thread->sig_block_mask);
context: has_signals_pending(void *_thread){	struct thread *thread = (struct thread *)_thread;	if (thread == NULL)		thread = thread_get_current_thread();	return thread->sig_pending & ~thread->sig_block_mask;}