fixed TargetArchs implementation in case when HAVE_CUDA=false, added initial structure for multi_gpu sample

samples/gpu/multi_gpu.cpp

@@ -0,0 +1,34 @@
+// Disable some warnings which are caused with CUDA headers
+#pragma warning(disable: 4201 4408 4100)
+
+#include <iostream>
+#include <cvconfig.h>
+#include <opencv2/gpu/gpu.hpp>
+#include <opencv2/highgui/highgui.hpp>
+
+#ifdef HAVE_CUDA
+#include <cuda_runtime.h>
+#endif
+
+using namespace std;
+using namespace cv;
+
+int main()
+{
+    bool can_run = true;
+
+#if !defined(HAVE_CUDA)
+    cout << "CUDA support is required (CMake key 'WITH_CUDA' must be true).\n";
+    can_run = false;
+#endif
+
+#if !defined(HAVE_TBB)
+    cout << "TBB support is required (CMake key 'WITH_TBB' must be true).\n";
+    can_run = false;
+#endif
+
+    if (!can_run)
+        return -1;
+
+    return 0;
+}