make pthread_create return EAGAIN on resource failure, as required by POSIX
diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c
index 72d7acb..d01be55 100644
--- a/src/thread/pthread_create.c
+++ b/src/thread/pthread_create.c
@@ -212,7 +212,7 @@
 	if (ret < 0) {
 		a_dec(&libc.threads_minus_1);
 		munmap(map, size);
-		return -ret;
+		return EAGAIN;
 	}
 	*res = new;
 	return 0;