[Ada] Reuse Is_Rewrite_Substitution in Relocate_Node

Semantics not affected; the reused routine is exactly the same as the replaced
condition.

2018-07-17  Piotr Trojanek  <trojanek@adacore.com>

gcc/ada/

	* atree.adb (Relocate_Node): Simplify with Is_Rewrite_Substitution.

From-SVN: r262799

gcc/ada/ChangeLog

 2018-07-17  Piotr Trojanek  <trojanek@adacore.com>
 
+	* atree.adb (Relocate_Node): Simplify with Is_Rewrite_Substitution.
+
+2018-07-17  Piotr Trojanek  <trojanek@adacore.com>
+
 	* sem_util.ads (Denotes_Same_Object): Likewise.
 	* sem_warn.adb (Warn_On_Overlapping_Actuals): Fix RM rule references.
 

gcc/ada/atree.adb

@@ -2186,7 +2186,7 @@ package body Atree is
       --  If the node being relocated was a rewriting of some original node,
       --  then the relocated node has the same original node.
 
-      if Orig_Nodes.Table (Source) /= Source then
+      if Is_Rewrite_Substitution (Source) then
          Orig_Nodes.Table (New_Node) := Orig_Nodes.Table (Source);
       end if;