temporarily disabled OpenCL use in DNN module on Mac (#11828)

* temporarily disabled OpenCL use in DNN module on Mac, since some of the tests fail

* disable OpenCL in DNN on Mac at CMake level, not source level (thanks to alalek for the advice)

modules/dnn/CMakeLists.txt

@@ -12,7 +12,8 @@ ocv_add_dispatched_file_force_all("layers/layers_common" AVX AVX2 AVX512_SKX)
 
 ocv_add_module(dnn opencv_core opencv_imgproc WRAP python matlab java js)
 
-ocv_option(OPENCV_DNN_OPENCL "Build with OpenCL support" HAVE_OPENCL)
+ocv_option(OPENCV_DNN_OPENCL "Build with OpenCL support" HAVE_OPENCL AND NOT APPLE)
+
 if(OPENCV_DNN_OPENCL AND HAVE_OPENCL)
   add_definitions(-DCV_OCL4DNN=1)
 else()