GDAL Fails to build when CUDA is installed

GDAL looks for OpenCL support in alg/CMakeLists.txt but doesn't add the correct include directories to be able to find the OpenCL headers.

This results in the following compile error:

In file included from /home/robert/Work/cmb_superbuild/build/superbuild/gdal/src/gdal/alg/gdalwarpkernel.cpp:35:
/home/robert/Work/cmb_superbuild/build/superbuild/gdal/src/gdal/alg/gdalwarpkernel_opencl.h:43:10: fatal error: 
      'CL/opencl.h' file not found
#include <CL/opencl.h>