Added concentric infill generated using Arachne.

src/libslic3r/Fill/FillConcentric.hpp

@@ -19,7 +19,18 @@ protected:
 	    ExPolygon     		             expolygon,
 	    Polylines                       &polylines_out) override;
 
-	bool no_sort() const override { return true; }
+    void _fill_surface_single(const FillParams              &params,
+                              unsigned int                   thickness_layers,
+                              const std::pair<float, Point> &direction,
+                              ExPolygon                      expolygon,
+                              ThickPolylines                &thick_polylines_out) override;
+
+    bool no_sort() const override { return true; }
+
+    const PrintConfig       *print_config        = nullptr;
+    const PrintObjectConfig *print_object_config = nullptr;
+
+    friend class Layer;
 };
 
 } // namespace Slic3r