Generic stop pins (presume one endstop per axis end)

Marlin/src/pins/pins.h

     #define X_MIN_PIN -1
     #define X_MAX_PIN X_STOP_PIN
   #endif
+#elif X_HOME_DIR < 0
+  #define X_STOP_PIN X_MIN_PIN
+#else
+  #define X_STOP_PIN X_MAX_PIN
 #endif
 
 #ifdef Y_STOP_PIN
     #define Y_MIN_PIN -1
     #define Y_MAX_PIN Y_STOP_PIN
   #endif
+#elif Y_HOME_DIR < 0
+  #define Y_STOP_PIN Y_MIN_PIN
+#else
+  #define Y_STOP_PIN Y_MAX_PIN
 #endif
 
 #ifdef Z_STOP_PIN
     #define Z_MIN_PIN -1
     #define Z_MAX_PIN Z_STOP_PIN
   #endif
+#elif Z_HOME_DIR < 0
+  #define Z_STOP_PIN Z_MIN_PIN
+#else
+  #define Z_STOP_PIN Z_MAX_PIN
 #endif
 
 //