Fix link issue with qa_pcbnew test.

I'm not terribly happy about the solution as it's a bit less safe.
But it's what we had before.

pcbnew/pcb_base_frame.cpp

@@ -114,7 +114,8 @@ PCB_BASE_FRAME::~PCB_BASE_FRAME()
 
 EDA_3D_VIEWER* PCB_BASE_FRAME::Get3DViewerFrame()
 {
-    return dynamic_cast<EDA_3D_VIEWER*>( FindWindow( VIEWER3D_FRAMENAME ) );
+    // Even though less safe, this has to be a static_cast so the qa tools will link.
+    return static_cast<EDA_3D_VIEWER*>( FindWindow( VIEWER3D_FRAMENAME ) );
 }