closes https://github.com/assimp/assimp/issues/1752: move guard over include statement.

code/Importer/IFC/IFCReaderGen_4.cpp

@@ -40,13 +40,14 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 /** MACHINE-GENERATED by scripts/ICFImporter/CppGenerator.py */
 
-#include "AssimpPCH.h"
 #ifndef ASSIMP_BUILD_NO_IFC_IMPORTER
 
-#include "IFCReaderGen.h"
+#include "AssimpPCH.h"
+#include "IFCReaderGen4.h"
 
 namespace Assimp {
 using namespace IFC;
+using namespace ::Assimp::IFC::Schema_4;
 
 namespace {