Provide a forward declaration for raw_cuda_device_buffer in cuda/copy_if.inl to fix broken trivial tests.
Provide a forward declaration for raw_cuda_device_buffer in cuda/copy_if.inl to fix broken trivial tests.

lishi0927/thrust,malenie/thrust,lishi0927/thrust,rdmenezes/thrust,rdmenezes/thrust,h1arshad/thrust,UIKit0/thrust,julianromera/thrust,rdmenezes/thrust,rdmenezes/thrust,malenie/thrust,lishi0927/thrust,Vishwa07/thrust,Vishwa07/thrust,Vishwa07/thrust,allendaicool/thrust,levendlee/thrust,Vishwa07/thrust,levendlee/thrust,hemmingway/thrust,UIKit0/thrust,bfurtaw/thrust,julianromera/thrust,julianromera/thrust,google-code-export/thrust,allendaicool/thrust,allendaicool/thrust,google-code-export/thrust,hemmingway/thrust,UIKit0/thrust,h1arshad/thrust,levendlee/thrust,h1arshad/thrust,lishi0927/thrust,google-code-export/thrust,malenie/thrust,allendaicool/thrust,julianromera/thrust,hemmingway/thrust,levendlee/thrust,bfurtaw/thrust,h1arshad/thrust,UIKit0/thrust,hemmingway/thrust,google-code-export/thrust,bfurtaw/thrust,malenie/thrust,bfurtaw/thrust