ada: Fixed elaboration of CUDA programs.

ada: Fixed elaboration of CUDA programs.

The names of imported / exported symbols were not consistent
between the device and the host when compiling for CUDA.

Remove the function Device_Ada_Final_Link_Name as it is no
longer referenced.

gcc/ada/

	* bindgen.adb: fixed the way the device init and final symbols are
	computed, re-using the normal way these symbols would be computed
	with a __device_ prefix. Also fixed the "is null;" procedure on
	the host side which are not Ada 95, replaced with a procedure
	raising an exception as it should never be called. Remove the
	unused function Device_Ada_Final_Link_Name.

Co-authored-by: Steve Baird <baird@adacore.com>