Backlash linker error workaround

Fix #14045

Marlin/src/feature/backlash.cpp

 #include "../module/motion.h"
 #include "../module/planner.h"
 
-#if ENABLED(BACKLASH_GCODE)
-  uint8_t Backlash::correction = (BACKLASH_CORRECTION) * 0xFF;
-  #ifdef BACKLASH_DISTANCE_MM
+#ifdef BACKLASH_DISTANCE_MM
+  #if ENABLED(BACKLASH_GCODE)
     float Backlash::distance_mm[XYZ] = BACKLASH_DISTANCE_MM;
+  #else
+    const float Backlash::distance_mm[XYZ] = BACKLASH_DISTANCE_MM;
   #endif
+#endif
+
+#if ENABLED(BACKLASH_GCODE)
+  uint8_t Backlash::correction = (BACKLASH_CORRECTION) * 0xFF;
   #ifdef BACKLASH_SMOOTHING_MM
     float Backlash::smoothing_mm = BACKLASH_SMOOTHING_MM;
   #endif

Marlin/src/feature/backlash.h

 
 class Backlash {
 public:
-  #if ENABLED(BACKLASH_GCODE)
-    static uint8_t correction;
-    #ifdef BACKLASH_DISTANCE_MM
+  #ifdef BACKLASH_DISTANCE_MM
+    #if ENABLED(BACKLASH_GCODE)
       static float distance_mm[XYZ];
+    #else
+      static const float distance_mm[XYZ];
+      //static constexpr float distance_mm[XYZ] = BACKLASH_DISTANCE_MM; // compiler barks at this
     #endif
+  #endif
+  #if ENABLED(BACKLASH_GCODE)
+    static uint8_t correction;
     #ifdef BACKLASH_SMOOTHING_MM
       static float smoothing_mm;
     #endif
     static inline float get_correction() { return float(ui8_to_percent(correction)) / 100.0f; }
   #else
     static constexpr uint8_t correction = (BACKLASH_CORRECTION) * 0xFF;
-    #ifdef BACKLASH_DISTANCE_MM
-      static constexpr float distance_mm[XYZ] = BACKLASH_DISTANCE_MM;
-    #endif
     #ifdef BACKLASH_SMOOTHING_MM
       static constexpr float smoothing_mm = BACKLASH_SMOOTHING_MM;
     #endif