Fix some overhang detection (#15694)

src/libslic3r/PerimeterGenerator.hpp

@@ -149,6 +149,8 @@ public:
     //BBS
     double      smaller_width_ext_mm3_per_mm()   const { return m_ext_mm3_per_mm_smaller_width; }
     Polygons    lower_slices_polygons() const { return m_lower_slices_polygons; }
+    // ORCA: the slices less the slivers the wall generator prints nothing for, so they never count as support.
+    ExPolygons  printable_slices(const ExPolygons &slices) const;
 
 private:
     std::vector<Polygons>     generate_lower_polygons_series(float width);