user defined data types in OpenCL

I want to use Opencl for double-double precision. I’ve found example on CUDA.
I how can I define a new data type typedef double2 gdd_real;(cuda definition)?
and and analogue host device for opencl?

cuda example
device host
gdd_real make_dd( const double x, const double y ) {
return make_double2( x, y );