ada: Optimize class-wide objects initialized with function calls

ada: Optimize class-wide objects initialized with function calls

This optimizes the implementation of class-wide objects initialized with
function calls in the non-interface case, by avoiding an unnecessary copy
operation and/or a dispatching call to the _Size primitive when possible.

gcc/ada/

	* exp_ch3.adb (Expand_N_Object_Declaration): New local variable
	Func_Id holding the function for a special return object.
	Use a direct renaming in the class-wide case when the initializing
	expression is a captured function call, except for a special return
	object when the two functions do not return on the same stack.
	Apply the accessibility check for class-wide special return objects.
	* exp_util.adb (Make_CW_Equivalent_Type) <Has_Tag_Of_Type>: New.
	Do not force a dispatching call to the primitive operation _Size if
	the expression is known to statically have the tag of its type.