[Ada] Reuse routines for detecting attributes Old and Result

[Pierre-Marie de Rodat <derodat@adacore.com>]

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Code cleanup related to handling of attribute 'Old in Contract_Cases;
semantics is unaffected.

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

gcc/ada/

	* exp_ch4.adb (Expand_N_Op_Eq): Reuse Is_Attribute_Result.
	* exp_prag.adb (Expand_Attributes): Reuse Is_Attribute_Old.

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diff --git a/gcc/ada/exp_ch4.adb b/gcc/ada/exp_ch4.adb
--- a/gcc/ada/exp_ch4.adb
+++ b/gcc/ada/exp_ch4.adb
@@ -8609,8 +8609,7 @@ package body Exp_Ch4 is
       --  f'Machine (expr) to eliminate surprise from extra precision.
 
       if Is_Floating_Point_Type (Typl)
-        and then Nkind (Original_Node (Lhs)) = N_Attribute_Reference
-        and then Attribute_Name (Original_Node (Lhs)) = Name_Result
+        and then Is_Attribute_Result (Original_Node (Lhs))
       then
          --  Stick in the Typ'Machine call if not already there
 


diff --git a/gcc/ada/exp_prag.adb b/gcc/ada/exp_prag.adb
--- a/gcc/ada/exp_prag.adb
+++ b/gcc/ada/exp_prag.adb
@@ -1525,9 +1525,7 @@ package body Exp_Prag is
          begin
             --  Attribute 'Old
 
-            if Nkind (N) = N_Attribute_Reference
-              and then Attribute_Name (N) = Name_Old
-            then
+            if Is_Attribute_Old (N) then
                Pref := Prefix (N);
 
                Indirect := Indirect_Temp_Needed (Etype (Pref));