[Ada] Implement initialization of CUDA runtime

[Ada] Implement initialization of CUDA runtime

gcc/ada/

	* debug.adb: Document -gnatd_c flag as being used for CUDA.
	* gnat_cuda.ads: New file.
	* gnat_cuda.adb: New file.
	* rtsfind.ads: Add Interfaces_C_Strings package and
	RE_Fatbin_Wrapper, RE_Register_Fat_Binary,
	RE_Register_Fat_Binary_End, RE_Register_Function, RE_Chars_Ptr,
	RE_New_Char_Array entities.
	* rtsfind.adb: Create new Interfaces_C_Descendant subtype,
	handle it.
	* sem_ch7.adb (Analyze_Package_Body_Helper): Call CUDA init
	procedure.
	* sem_prag.adb (Analyze_Pragma): Call Add_Cuda_Kernel procedure.
	* gcc-interface/Make-lang.in (GNAT_ADA_OBJS): Add gnat_cuda.o.