cmake: fix build process of OpenCL kernels

cmake/OpenCVModule.cmake

@@ -720,11 +720,16 @@ macro(ocv_glob_module_sources)
   if(cl_kernels)
     set(OCL_NAME opencl_kernels_${name})
     add_custom_command(
-      OUTPUT "${CMAKE_CURRENT_BINARY_DIR}/${OCL_NAME}.hpp" "${CMAKE_CURRENT_BINARY_DIR}/${OCL_NAME}.cpp"
+      OUTPUT "${CMAKE_CURRENT_BINARY_DIR}/${OCL_NAME}.cpp"  # don't add .hpp file here to optimize build process
       COMMAND ${CMAKE_COMMAND} "-DMODULE_NAME=${name}" "-DCL_DIR=${CMAKE_CURRENT_LIST_DIR}/src/opencl" "-DOUTPUT=${CMAKE_CURRENT_BINARY_DIR}/${OCL_NAME}.cpp" -P "${OpenCV_SOURCE_DIR}/cmake/cl2cpp.cmake"
-      DEPENDS ${cl_kernels} "${OpenCV_SOURCE_DIR}/cmake/cl2cpp.cmake")
+      DEPENDS ${cl_kernels} "${OpenCV_SOURCE_DIR}/cmake/cl2cpp.cmake"
+      COMMENT "Processing OpenCL kernels (${name})"
+    )
     ocv_source_group("Src\\opencl\\kernels" FILES ${cl_kernels})
     ocv_source_group("Src\\opencl\\kernels\\autogenerated" FILES "${CMAKE_CURRENT_BINARY_DIR}/${OCL_NAME}.cpp" "${CMAKE_CURRENT_BINARY_DIR}/${OCL_NAME}.hpp")
+    set_source_files_properties("${CMAKE_CURRENT_BINARY_DIR}/${OCL_NAME}.cpp" "${CMAKE_CURRENT_BINARY_DIR}/${OCL_NAME}.hpp"
+        PROPERTIES GENERATED TRUE
+    )
     list(APPEND lib_srcs ${cl_kernels} "${CMAKE_CURRENT_BINARY_DIR}/${OCL_NAME}.cpp" "${CMAKE_CURRENT_BINARY_DIR}/${OCL_NAME}.hpp")
   endif()