Turns out it is possible to have code to pick up wrong class
when defining a friend:
```
intern\cycles\device/memory.h(255): warning C4099: 'GPUDevice': type name first seen using 'struct' now seen using 'class'
source\blender\gpu\GPU_platform.hh(69): note: see declaration of 'GPUDevice'
```
Now made it so the classes have forward declaration in the CCL
namespace, avoiding possible conflict with the classes with the
same name in the global namespace.
Pull Request: https://projects.blender.org/blender/blender/pulls/128485
6c3f3a7fb6