Cleanup the public headers.

include/assimp/SGSpatialSort.h

@@ -42,9 +42,14 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 /** Small helper classes to optimize finding vertices close to a given location
  */
+#pragma once
 #ifndef AI_D3DSSPATIALSORT_H_INC
 #define AI_D3DSSPATIALSORT_H_INC
 
+#ifdef __GNUC__
+#   pragma GCC system_header
+#endif
+
 #include <assimp/types.h>
 #include <vector>
 #include <stdint.h>