message: fixe class export compiling issue
diff: @@ -185,7 +185,7 @@ namespace RINGMesh {
  RockFeature rock_;
  };
  - class UnsubdividedStratigraphicUnit: public StratigraphicUnit {
  + class RINGMESH_API UnsubdividedStratigraphicUnit: public StratigraphicUnit {
  public:
  UnsubdividedStratigraphicUnit(
  @@ -251,7 +251,7 @@ namespace RINGMesh {
  double max_thick_;
  };
  - class SubdividedStratigraphicUnit: public StratigraphicUnit {
  + class RINGMESH_API SubdividedStratigraphicUnit: public StratigraphicUnit {
  public:
  SubdividedStratigraphicUnit(
  