Try to find OpenCL

Once done this will define:

OpenCL_FOUND          - True if OpenCL was found
OpenCL_INCLUDE_DIRS   - include directories for OpenCL
OpenCL_LIBRARIES      - link against this library to use OpenCL
OpenCL_VERSION_STRING - Highest supported OpenCL version (eg. 1.2)
OpenCL_VERSION_MAJOR  - The major version of the OpenCL implementation
OpenCL_VERSION_MINOR  - The minor version of the OpenCL implementation

The module will also define two cache variables:

OpenCL_INCLUDE_DIR    - the OpenCL include directory
OpenCL_LIBRARY        - the path to the OpenCL library