[Ada] Simplify conversions from Uint to Char_Code

[Pierre-Marie de Rodat via Gcc-patches]

Replace "Char_Code (UI_To_Int (...))" with "UI_To_CC (...).

Cleanup related to handling characters in GNATprove counterexamples;
semantics is unaffected.

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

gcc/ada/

        * par-prag.adb (Prag): Simplify conversion of character codes.
        * sem_case.adb (Choice_Image): Likewise.
        (Lit_Of): Likewise.
diff --git a/gcc/ada/par-prag.adb b/gcc/ada/par-prag.adb
--- a/gcc/ada/par-prag.adb
+++ b/gcc/ada/par-prag.adb
@@ -1266,8 +1266,7 @@ begin
 
          elsif Nkind (A) = N_Character_Literal then
             declare
-               R : constant Char_Code :=
-                     Char_Code (UI_To_Int (Char_Literal_Value (A)));
+               R : constant Char_Code := UI_To_CC (Char_Literal_Value (A));
             begin
                if In_Character_Range (R) then
                   Wide_Character_Encoding_Method :=


diff --git a/gcc/ada/sem_case.adb b/gcc/ada/sem_case.adb
--- a/gcc/ada/sem_case.adb
+++ b/gcc/ada/sem_case.adb
@@ -1104,7 +1104,7 @@ package body Sem_Case is
          C := UI_To_Int (Value);
 
          if C in 16#20# .. 16#7E# then
-            Set_Character_Literal_Name (Char_Code (UI_To_Int (Value)));
+            Set_Character_Literal_Name (UI_To_CC (Value));
             return Name_Find;
          end if;
 
@@ -2925,7 +2925,7 @@ package body Sem_Case is
          --  is created with the appropriate Char_Code and Chars fields.
 
          if Is_Standard_Character_Type (Choice_Type) then
-            Set_Character_Literal_Name (Char_Code (UI_To_Int (Value)));
+            Set_Character_Literal_Name (UI_To_CC (Value));
             Lit :=
               Make_Character_Literal (Loc,
                 Chars              => Name_Find,