ada: Fix fallout of change to 'Wide_Wide_Value for enumeration types

ada: Fix fallout of change to 'Wide_Wide_Value for enumeration types

The literals of enumeration types are always normalized, even though they
contain wide characters (but the normalization leaves these unchanged),
so a normalization routine that is aware of wide characters must be run
on the input string for 'Wide_Wide_Value.

gcc/ada/ChangeLog:

	PR ada/115507
	* rtsfind.ads (RE_Id): Add RE_Enum_[Wide_]Wide_String_To_String.
	(RE_Unit_Table): Add entries for the new values.
	* exp_attr.adb (Is_User_Defined_Enumeration_Type): New predicate.
	(Expand_N_Attribute_Reference) <Attribute_Wide_Value>: Build a call
	to RE_Enum_Wide_String_To_String for user-defined enumeration types.
	<Attribute_Wide_Wide_Value>: Likewise with
	RE_Enum_Wide_Wide_String_To_String.
	* exp_imgv.adb (Expand_Value_Attribute): Adjust to above.
	* libgnat/s-wchwts.ads (Enum_Wide_String_To_String): New function.
	(Enum_Wide_Wide_String_To_String): Likewise.
	* libgnat/s-wchwts.adb: Add clauses for System.Case_Util.
	(Normalize_String): New local procedure.
	(Enum_Wide_String_To_String): New function body.
	(Enum_Wide_Wide_String_To_String): Likewise.