fix compile errors

src/libslic3r/GCode.hpp

@@ -138,6 +138,20 @@ public:
     static const std::vector<std::string>& get() { return Colors; }
 };
 
+struct LayerResult {
+    std::string gcode;
+    size_t      layer_id;
+    // Is spiral vase post processing enabled for this layer?
+    bool        spiral_vase_enable { false };
+    // Should the cooling buffer content be flushed at the end of this layer?
+    bool        cooling_buffer_flush { false };
+    // Is indicating if this LayerResult should be processed, or it is just inserted artificial LayerResult.
+    // It is used for the pressure equalizer because it needs to buffer one layer back.
+    bool        nop_layer_result { false };
+
+    static LayerResult make_nop_layer_result() { return {"", std::numeric_limits<coord_t>::max(), false, false, true}; }
+};
+
 class GCode {
 public:
     GCode() :