Replace c_assert hack with static_assert

Marlin/configuration_store.cpp

@@ -339,7 +339,10 @@ void MarlinSettings::postprocess() {
 
     #if ENABLED(MESH_BED_LEVELING)
       // Compile time test that sizeof(mbl.z_values) is as expected
-      typedef char c_assert[(sizeof(mbl.z_values) == (GRID_MAX_POINTS_X) * (GRID_MAX_POINTS_Y) * sizeof(dummy)) ? 1 : -1];
+      static_assert(
+        sizeof(mbl.z_values) == (GRID_MAX_POINTS_X) * (GRID_MAX_POINTS_Y) * sizeof(mbl.z_values[0][0]),
+        "MBL Z array is the wrong size."
+      );
       const bool leveling_is_on = TEST(mbl.status, MBL_STATUS_HAS_MESH_BIT);
       const uint8_t mesh_num_x = GRID_MAX_POINTS_X, mesh_num_y = GRID_MAX_POINTS_Y;
       EEPROM_WRITE(leveling_is_on);
@@ -381,7 +384,10 @@ void MarlinSettings::postprocess() {
 
     #if ENABLED(AUTO_BED_LEVELING_BILINEAR)
       // Compile time test that sizeof(bed_level_grid) is as expected
-      typedef char c_assert[(sizeof(bed_level_grid) == (GRID_MAX_POINTS_X) * (GRID_MAX_POINTS_Y) * sizeof(dummy)) ? 1 : -1];
+      static_assert(
+        sizeof(bed_level_grid) == (GRID_MAX_POINTS_X) * (GRID_MAX_POINTS_Y) * sizeof(bed_level_grid[0][0]),
+        "Bilinear Z array is the wrong size."
+      );
       const uint8_t grid_max_x = GRID_MAX_POINTS_X, grid_max_y = GRID_MAX_POINTS_Y;
       EEPROM_WRITE(grid_max_x);            // 1 byte
       EEPROM_WRITE(grid_max_y);            // 1 byte