lib9: fix Mac warning

R=rsc
http://codereview.appspot.com/6749053
diff --git a/src/lib9/dirread.c b/src/lib9/dirread.c
index 30a9065..0e38db3 100644
--- a/src/lib9/dirread.c
+++ b/src/lib9/dirread.c
@@ -18,7 +18,14 @@
 	nn = getdirentries(fd, (void*)buf, n, &off);
 	return nn;
 }
-#elif defined(__APPLE__) || defined(__FreeBSD__) || defined(__OpenBSD__)
+#elif defined(__APPLE__) 
+static int
+mygetdents(int fd, struct dirent *buf, int n)
+{
+	long off;
+	return getdirentries(fd, (void*)buf, n, &off);
+}
+#elif defined(__FreeBSD__) || defined(__OpenBSD__)
 static int
 mygetdents(int fd, struct dirent *buf, int n)
 {