libc: set malloctag for runestrdup()

sys/src/libc/port/runestrdup.c

@@ -9,6 +9,6 @@ runestrdup(Rune *s)
 	ns = malloc(sizeof(Rune)*(runestrlen(s) + 1));
 	if(ns == 0)
 		return 0;
-
+	setmalloctag(ns, getcallerpc(&s));
 	return runestrcpy(ns, s);
 }