Add some virtual destructors

pcbnew/drc/courtyard_overlap.h

@@ -37,7 +37,9 @@ class DRC_COURTYARD_OVERLAP : public DRC_TEST_PROVIDER
 public:
     DRC_COURTYARD_OVERLAP( MARKER_HANDLER aMarkerHandler );
 
+    virtual ~DRC_COURTYARD_OVERLAP() {};
+
     bool RunDRC( BOARD& aBoard ) const override;
 };
 
-#endif // DRC_COURTYARD_OVERLAP__H
+#endif // DRC_COURTYARD_OVERLAP__H

pcbnew/drc/drc_provider.h

@@ -52,6 +52,8 @@ public:
      */
     virtual bool RunDRC( BOARD& aBoard ) const = 0;
 
+    virtual ~DRC_TEST_PROVIDER() {}
+
 protected:
     DRC_TEST_PROVIDER( MARKER_HANDLER aMarkerHandler ) :
             m_marker_handler( std::move( aMarkerHandler ) )
@@ -278,4 +280,4 @@ public:
 };
 
 
-#endif // DRC_PROVIDER__H
+#endif // DRC_PROVIDER__H