Fix nameless union initialization.

[Kerilk]

This should address the issue generated by KhronosGroup/OpenCL-Headers#280.
If we want backward compatibility, we should do some version detection to address both cases.

Error was, for reference:

/__w/OpenCL-ICD-Loader/OpenCL-ICD-Loader/loader/icd_dispatch_generated.c:6828:5: error: suggest braces around initialization of subobject [-Werror,-Wmissing-braces]
    &clGetPlatformIDs_disp,
    ^~~~~~~~~~~~~~~~~~~~~~
    {                     }

[bashbaug]

Merging - this is needed to build with the latest headers.