DM: update feather m4 pinout for new rev

Author: deanm1278

cores/arduino/WVariant.h

@@ -20,6 +20,7 @@
 
 #include <stdint.h>
 #include "sam.h"
+#include <limits.h>
 
 #ifdef __cplusplus
 extern "C" {
@@ -186,6 +187,8 @@ typedef enum _EPortType
   PORTC=2,
 } EPortType ;
 
+#define PIN_NOT_A_PIN (UINT_MAX)
+
 typedef enum
 {
   EXTERNAL_INT_0 = 0,