2013-04-26  Marcelo Morais  <m.morais@samsung.com>

        Handling userData properly before send it to buildProgram.

        Reviewed by Antonio Gomes.

        On linux build with a NVIDIA graphic card and OpenCL 1.1,
        if there is no callback and the userData is passed, even
        if its value is zero, it won't be considered as a null
        pointer because of the gcc casting and an exception is
        raised. According to OpenCL specification if there is no
        callback the userData must be null. On Mac build this is not
        necessary because CLang compiler handles casting differently.

        * Modules/webcl/WebCLProgram.cpp:
        (WebCore::WebCLProgram::build):