Sanity-check CORE backlash axes (#17279)

Co-authored-by: Scott Lahteine <thinkyhead@users.noreply.github.com>

Marlin/src/inc/SanityCheck.h

@@ -2651,14 +2651,14 @@ static_assert(   _ARR_TEST(3,0) && _ARR_TEST(3,1) && _ARR_TEST(3,2)
 #endif
 
 #if ENABLED(BACKLASH_COMPENSATION)
-  #if IS_CORE
-    #error "BACKLASH_COMPENSATION is incompatible with CORE kinematics."
-  #endif
   #ifndef BACKLASH_DISTANCE_MM
     #error "BACKLASH_COMPENSATION requires BACKLASH_DISTANCE_MM"
-  #endif
+  #elif !defined(BACKLASH_CORRECTION)
-  #ifndef BACKLASH_CORRECTION
     #error "BACKLASH_COMPENSATION requires BACKLASH_CORRECTION"
+  #elif IS_CORE
+    constexpr float backlash_arr[] = BACKLASH_DISTANCE_MM;
+    static_assert(!backlash_arr[CORE_AXIS_1] && !backlash_arr[CORE_AXIS_2],
+                  "BACKLASH_COMPENSATION can only apply to " STRINGIFY(NORMAL_AXIS) " with your CORE system.");
   #endif
 #endif