Get cudalegacy dependents to build without CUDA

Author: vrabaud

modules/cudalegacy/include/opencv2/cudalegacy/private.hpp

@@ -50,9 +50,7 @@
 
 #include "opencv2/core/private.cuda.hpp"
 
-#ifndef HAVE_CUDA
-#  error cudalegacy module requires CUDA
-#endif
+#ifdef HAVE_CUDA
 
 #include "opencv2/cudalegacy.hpp"
 
@@ -93,4 +91,6 @@ namespace cv { namespace cuda
 
 //! @endcond
 
+#endif HAVE_CUDA
+
 #endif // OPENCV_CORE_CUDALEGACY_PRIVATE_HPP