[Ada] Stub CUDA_Execute and CUDA_Global pragmas

[Ada] Stub CUDA_Execute and CUDA_Global pragmas

This commit adds CUDA_Execute and CUDA_Global to the list of allowed
pragmas. It also implements basic validation of said pragmas.

gcc/ada/

	* aspects.ads: Declare CUDA_Global as aspect.
	* einfo.ads: Use Flag118 for the Is_CUDA_Kernel flag.
	(Set_Is_CUDA_Kernel): New function.
	(Is_CUDA_Kernel): New function.
	* einfo.adb (Set_Is_CUDA_Kernel): New function.
	(Is_CUDA_Kernel): New function.
	* par-prag.adb (Prag): Ignore Pragma_CUDA_Execute and
	Pragma_CUDA_global.
	* rtsfind.ads: Define CUDA.Driver_Types.Stream_T and
	CUDA.Vector_Types.Dim3 entities
	* rtsfind.adb: Define CUDA_Descendant subtype.
	(Get_Unit_Name): Handle CUDA_Descendant packages.
	* sem_prag.ads: Mark CUDA_Global as aspect-specifying pragma.
	* sem_prag.adb (Analyze_Pragma): Validate Pragma_CUDA_Execute and
	Pragma_CUDA_Global.
	* snames.ads-tmpl: Define Name_CUDA_Execute and Name_CUDA_Global.