ada: Put_Image aspect spec ignored for null extension.

ada: Put_Image aspect spec ignored for null extension.

If type T1 is is a tagged null record with a Put_Image aspect specification
and type T2 is a null extension of T1 (with no aspect specifications), then
evaluation of a T2'Image call should include a call to the specified procedure
(as opposed to yielding "(NULL RECORD)").

gcc/ada/

	* exp_put_image.adb
	(Build_Record_Put_Image_Procedure): Declare new Boolean-valued
	function Null_Record_Default_Implementation_OK; call it as part of
	deciding whether to generate "(NULL RECORD)" text.