[Ada] Stub CUDA_Device aspect

[Ada] Stub CUDA_Device aspect

gcc/ada/

	* aspects.ads: Add CUDA_Device aspect.
	* gnat_cuda.ads (Add_CUDA_Device_Entity): New subprogram.
	* gnat_cuda.adb:
	(Add_CUDA_Device_Entity): New subprogram.
	(CUDA_Device_Entities_Table): New hashmap for CUDA_Device
	entities.
	(Get_CUDA_Device_Entities): New internal subprogram.
	(Set_CUDA_Device_Entities): New internal subprogram.
	* par-prag.adb (Prag): Handle pragma id Pragma_CUDA_Device.
	* sem_prag.ads (Aspect_Specifying_Pragma): Mark CUDA_Device as
	being both aspect and pragma.
	* sem_prag.adb (Analyze_Pragma): Add CUDA_Device entities to
	list of CUDA_Entities belonging to package N.
	(Sig_Flags): Signal CUDA_Device entities as referenced.
	* snames.ads-tmpl: Create CUDA_Device names and pragmas.