Automatically set X2 stepper pins

Marlin/macros.h

@@ -55,6 +55,32 @@
 #define NUMERIC_SIGNED(a) (NUMERIC(a) || (a) == '-')
 #define COUNT(a) (sizeof(a)/sizeof(*a))
 
+// Macros for adding
+#define INC_0 1
+#define INC_1 2
+#define INC_2 3
+#define INC_3 4
+#define INC_4 5
+#define INC_5 6
+#define INC_6 7
+#define INC_7 8
+#define INC_8 9
+#define INCREMENT_(n) INC_ ##n
+#define INCREMENT(n) INCREMENT_(n)
+
+// Macros for subtracting
+#define DEC_1 0
+#define DEC_2 1
+#define DEC_3 2
+#define DEC_4 3
+#define DEC_5 4
+#define DEC_6 5
+#define DEC_7 6
+#define DEC_8 7
+#define DEC_9 8
+#define DECREMENT_(n) DEC_ ##n
+#define DECREMENT(n) DECREMENT_(n)
+
 #define PIN_EXISTS(PN) (defined(PN ##_PIN) && PN ##_PIN >= 0)
 
 #define PENDING(NOW,SOON) ((long)(NOW-(SOON))<0)