core/sched: Add missing inttypes.h include when debugging.

core/sched.c

@@ -38,6 +38,11 @@
 #define ENABLE_DEBUG (0)
 #include "debug.h"
 
+#if ENABLE_DEBUG
+/* For PRIu16 etc. */
+#include <inttypes.h>
+#endif
+
 volatile int sched_num_threads = 0;
 
 volatile unsigned int sched_context_switch_request;