ada: Fix internal error on instantiation with private component type

ada: Fix internal error on instantiation with private component type

First, this fixes an internal error on the instantiation of a nested generic
package taking an array type whose component type is a private type declared
in the parent package as formal type parameter. In the body of the instance,
the full view of the private type is visible and must be restored by means
of the Check_Generic_Actuals mechanism.

Second, this fixes the same internal error in the case where the component
type itself is an array type whose component type is a private type declared
in the parent package, i.e. when the formal type parameter is an array of
array type, by naturally extending the Has_Secondary_Private_View mechanism
to the array of array case.

gcc/ada/

	* sem_ch12.adb (Component_Type_For_Private_View): New function.
	(Check_Generic_Actuals): For an actual type parameter, also check
	its component type if it is an array type.
	(Check_Private_View): Use Component_Type_For_Private_View in the
	case of an array type.
	(Instantiate_Type): Likewise.
	(Save_Global_References.Set_Global_Type): Likewise.