[Ada] Reuse existing To_Mixed routine in pretty-printer

[Pierre-Marie de Rodat]

Unit Pprint, which implements pretty-printing of the AST, defined
routine To_Mixed_Case, which was identical to System.Case_Util.To_Mixed.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

        * pprint.adb (To_Mixed): Removed.
diff --git a/gcc/ada/pprint.adb b/gcc/ada/pprint.adb
--- a/gcc/ada/pprint.adb
+++ b/gcc/ada/pprint.adb
@@ -24,7 +24,6 @@
 ------------------------------------------------------------------------------
 
 with Atree;   use Atree;
-with Csets;   use Csets;
 with Einfo;   use Einfo;
 with Namet;   use Namet;
 with Nlists;  use Nlists;
@@ -34,6 +33,8 @@ with Sinput;  use Sinput;
 with Snames;  use Snames;
 with Uintp;   use Uintp;
 
+with System.Case_Util;
+
 package body Pprint is
 
    List_Name_Count : Natural := 0;
@@ -272,32 +273,6 @@ package body Pprint is
             when N_Attribute_Reference =>
                if Take_Prefix then
                   declare
-                     function To_Mixed_Case (S : String) return String;
-                     --  Transform given string into the corresponding one in
-                     --  mixed case form.
-
-                     -------------------
-                     -- To_Mixed_Case --
-                     -------------------
-
-                     function To_Mixed_Case (S : String) return String is
-                        Result : String (S'Range);
-                        Ucase  : Boolean := True;
-
-                     begin
-                        for J in S'Range loop
-                           if Ucase then
-                              Result (J) := Fold_Upper (S (J));
-                           else
-                              Result (J) := Fold_Lower (S (J));
-                           end if;
-
-                           Ucase := (S (J) = '_');
-                        end loop;
-
-                        return Result;
-                     end To_Mixed_Case;
-
                      Id : constant Attribute_Id :=
                             Get_Attribute_Id (Attribute_Name (Expr));
 
@@ -306,7 +281,7 @@ package body Pprint is
                      Str : constant String :=
                              Expr_Name (Prefix (Expr))
                                & "'"
-                               & To_Mixed_Case
+                               & System.Case_Util.To_Mixed
                                    (Get_Name_String (Attribute_Name (Expr)));
 
                      N      : Node_Id;