build: eliminate GCC8 warnings

apps/createsamples/utility.cpp

@@ -54,6 +54,10 @@
 #include "opencv2/highgui.hpp"
 #include "opencv2/calib3d.hpp"
 
+#if defined __GNUC__ && __GNUC__ >= 8
+#pragma GCC diagnostic ignored "-Wclass-memaccess"
+#endif
+
 using namespace cv;
 
 #ifndef PATH_MAX