tests: Add mssing includes for leds and xtimer test

tests/leds/main.c

@@ -19,6 +19,7 @@
  */
 
 #include <stdio.h>
+#include <stdint.h>
 
 #include "board.h"
 #include "periph_conf.h"

tests/xtimer_msg_receive_timeout/main.c

@@ -23,6 +23,7 @@
  *
  * @}
  */
+#include <stdio.h>
 
 #include "thread.h"
 #include "msg.h"