message: more compile fixes
diff: #pragma once
  +#include "sg/SceneGraphExports.h"
  #include "sg/common/Common.h"
  // ospcommon
  #include "ospcommon/AffineSpace.h"
  @@ -40,7 +41,7 @@ namespace ospray {
  DONT_FOLLOW_INSTANCES
  } Mode;
  - struct Instantiation {
  + struct OSPSG_INTERFACE Instantiation {
  std::shared_ptr<Instantiation> parentWorld;
  affine3f xfm;
  