suppress noisy warning

  * limit the affect by using HAVE_CUDA

modules/hfs/CMakeLists.txt

 if(HAVE_CUDA)
   add_definitions(-D_HFS_CUDA_ON_)
+  ocv_warnings_disable(CMAKE_CXX_FLAGS -Wundef)
 endif()
 
 set(the_description "Hierarchical Feature Selection for Efficient Image Segmentation")

modules/xfeatures2d/CMakeLists.txt

 set(the_description "Contributed/Experimental Algorithms for Salient 2D Features Detection")
 
+if(HAVE_CUDA)
+  ocv_warnings_disable(CMAKE_CXX_FLAGS -Wundef)
+endif()
 ocv_define_module(xfeatures2d opencv_core opencv_imgproc opencv_features2d opencv_calib3d OPTIONAL opencv_shape opencv_ml opencv_cudaarithm WRAP python java)
 
 include(${CMAKE_CURRENT_SOURCE_DIR}/cmake/download_vgg.cmake)