[Ada] AI12-0397: Default_Initial_Condition expressions for derived types

[Ada] AI12-0397: Default_Initial_Condition expressions for derived types

gcc/ada/

	* exp_util.adb (Add_Own_DIC): Suppress expansion of a DIC pragma
	when the pragma occurs for an abstract type, since that could
	lead to a call to an abstract function, and such DIC checks can
	never be performed for abstract types in any case.
	* sem_disp.adb (Check_Dispatching_Context): Suppress the check
	for illegal calls to abstract subprograms when the call occurs
	within a Default_Initial_Condition aspect and the call is passed
	the current instance as an actual.
	(Has_Controlling_Current_Instance_Actual): New function to test
	a call to see if it has any actuals given by direct references
	to a current instance of a type
	* sem_res.adb (Resolve_Actuals): Issue an error for a call
	within a DIC aspect to a nonprimitive subprogram with an actual
	given by the name of the DIC type's current instance (which will
	show up as a reference to the formal parameter of a DIC
	procedure).