Update matrix4x4.h (#5507)

Co-authored-by: Kim Kulling <[email protected]>

include/assimp/matrix4x4.h

@@ -53,6 +53,7 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #include <assimp/vector3.h>
 #include <assimp/defs.h>
+#include <assimp/config.h>
 
 #ifdef __cplusplus