clRNG.clh:79:34: error: variadic macros not supported in OpenCL

Hello.

Both beignet and neo Intel drivers do not support variadic macros, so
`
#define clrngSetErrorString(err, ...) (err)
`
does not compile.

I suggest to introduce clrngSetErrorString2 and clrngSetErrorString3 macros to address errors with and without one extra argument. Should I prepare a merge request?