Tests/CudaOnly/DeviceLTO/file2.cu - third_party/github.com/Kitware/CMake - Git at Google

 extern __device__ int file3_func(int);
 int __device__ file2_func(int x)
 {
   return x + file3_func(x);
 }
	extern __device__ int file3_func(int);
	int __device__ file2_func(int x)
	{
	return x + file3_func(x);
	}