Property definitions

pthreads $ NativePthread :: create
	new create(nit_thread: Thread) import Thread.main_intern `{
		pthread_attr_t attr;
		pthread_attr_init(&attr);

		pthread_t thread;
		int r = pthread_create(&thread, &attr, (void * (*)(void *))&Thread_main_intern, nit_thread);

		if (r == 0) {
			pthread_t *pthread = malloc(sizeof(pthread_t));
			memmove(pthread, &thread, sizeof(pthread_t));
			return pthread;
		}
		return NULL;
	`}
lib/pthreads/pthreads.nit:141,2--154,3