Put #ifdef around servo pins in pins.h. This allows the pins to be used for M42.

Marlin/pins.h

@@ -375,10 +375,18 @@
 #define HEATER_BED_PIN     8    // BED
 #define TEMP_BED_PIN       14   // ANALOG NUMBERING
 
-#define SERVO0_PIN         11
+#ifdef NUM_SERVOS
-#define SERVO1_PIN         6
+  #define SERVO0_PIN         11
-#define SERVO2_PIN         5
+  #if NUM_SERVOS > 1
-#define SERVO3_PIN         4
+  #define SERVO1_PIN         6
+  #endif
+  #if NUM_SERVOS > 2
+  #define SERVO2_PIN         5
+  #endif
+  #if NUM_SERVOS > 2
+  #define SERVO3_PIN         4
+  #endif
+#endif
 
 #ifdef ULTRA_LCD