[Ada] Wrong renaming of variant record equality

[Ada] Wrong renaming of variant record equality

For a renaming of the equality operator of a variant record the compiler
erroneously generates code that compares all the record component (thus
computing wrong results).

After this patch the following test provides the correct results.

package Types is
   type Data (Bool : Boolean := False) is record
      case Bool is
         when False =>
            null;

         when True =>
            Val1 : Integer range 0 .. 2 ** 23 - 1;
            Val2 : Float;
      end case;
   end record;

   function IsEqual (Left, Right : Data) return Boolean renames "=";
end Types;

with Types;
with Ada.Text_IO;
procedure Main is
   A : Types.Data := Types.Data'(Bool => True,
                                 Val1 => 16#05A5A5#,
                                 Val2 => 999999999.0);

   B : Types.Data := Types.Data'(Bool => True,
                                 Val1 => 16#0A5A5A#,
                                 Val2 => 6666666666.0);
   use type Types.Data;
begin
   A := (Bool => False);             --  Test
   B := (Bool => False);             --  Test

   if Types.IsEqual (A, B) then      --  Test
      Ada.Text_IO.Put_Line ("OK");
   else
      Ada.Text_IO.Put_Line ("ERROR");
   end if;
end Main;

Command: gnatmake main; ./main
 Output: OK

2018-05-24  Javier Miranda  <miranda@adacore.com>

gcc/ada/

	* exp_ch8.adb (Build_Body_For_Renaming): Adding support to build the
	body of a variant record equality renaming.
	(Expand_N_Subprogram_Renaming_Declaration): Adapt the code to the new
	implementation of Build_Body_For_Renaming.
	* exp_ch3.ads (Build_Variant_Record_Equality): New library level
	function that factorizes the functionality needed by
	Build_Body_For_Renaming and Expand_Freeze_Record_Type to build the body
	of a variant record equality subprogram.
	* exp_ch3.adb (Build_Variant_Record_Equality): New subprogram.
	(Build_Variant_Record_Equality): New local procedure of
	Expand_Freeze_Record_Type containing all the code specific for freezing
	the record type that cannot be place in the new library level function.

From-SVN: r260667