[Ada] Remove discriminant checks processing in gigi

[Ada] Remove discriminant checks processing in gigi

gcc/ada/

	* sem_ch4.adb (Analyze_Selected_Component): Request a compile
	time error replacement in Apply_Compile_Time_Constraint_Error
	in case of an invalid field.
	* sem_ch3.adb (Create_Constrained_Components): Take advantage of
	Gather_Components also in the case of a record extension and
	also constrain records in the case of compile time known discriminant
	values, as already done in gigi.
	* sem_util.ads, sem_util.adb (Gather_Components): New parameter
	Allow_Compile_Time to allow compile time known (but non static)
	discriminant values, needed by Create_Constrained_Components,
	and new parameter Include_Interface_Tag.
	(Is_Dependent_Component_Of_Mutable_Object): Use Original_Node to
	perform check on the original tree.
	(Is_Object_Reference): Likewise.  Only call Original_Node when
	relevant via a new function Safe_Prefix.
	(Is_Static_Discriminant_Component, In_Check_Node): New.
	(Is_Actual_Out_Or_In_Out_Parameter): New.
	* exp_ch4.adb (Expand_N_Selected_Component): Remove no longer needed
	code preventing evaluating statically discriminants in more cases.
	* exp_ch5.adb (Expand_N_Loop_Statement): Simplify expansion of loops
	with an N_Raise_xxx_Error node to avoid confusing the code generator.
	(Make_Component_List_Assign): Try to find a constrained type to
	extract discriminant values from, so that the case statement
	built gets an opportunity to be folded by
	Expand_N_Case_Statement.
	(Expand_Assign_Record): Update comments, code cleanups.
	* sem_attr.adb (Analyze_Attribute): Perform most of the analysis
	on the original prefix node to deal properly with a prefix rewritten
	as a N_Raise_xxx_Error.
	* sem_ch5.adb (Analyze_Loop_Parameter_Specification): Handle properly
	a discrete subtype definition being rewritten as N_Raise_xxx_Error.
	* sem_ch8.adb (Analyze_Object_Renaming): Handle N_Raise_xxx_Error
	nodes as part of the expression being renamed.
	* sem_eval.ads, sem_eval.adb (Fold, Eval_Selected_Component): New.
	(Compile_Time_Known_Value, Expr_Value, Expr_Rep_Value): Evaluate
	static discriminant component values.
	* sem_res.adb (Resolve_Selected_Component): Call
	Eval_Selected_Component.