[Ada] Refactor repeated call to Next when pretty-printing if-expressions

[Pierre-Marie de Rodat]

Code cleanup (and minuscule performance improvement); semantics is
unaffected.

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

gcc/ada/

        * pprint.adb (Expr_Name): Introduce local constants to make the
        code more readable and avoid repeated calls to Next to reach the
        ELSE part of an if-expression.
diff --git a/gcc/ada/pprint.adb b/gcc/ada/pprint.adb
--- a/gcc/ada/pprint.adb
+++ b/gcc/ada/pprint.adb
@@ -410,12 +410,14 @@ package body Pprint is
 
             when N_If_Expression =>
                declare
-                  N : constant Node_Id := First (Expressions (Expr));
+                  Cond_Expr : constant Node_Id := First (Expressions (Expr));
+                  Then_Expr : constant Node_Id := Next (Cond_Expr);
+                  Else_Expr : constant Node_Id := Next (Then_Expr);
                begin
                   return
-                    "if " & Expr_Name (N) & " then "
-                      & Expr_Name (Next (N)) & " else "
-                      & Expr_Name (Next (Next (N)));
+                    "if " & Expr_Name (Cond_Expr) & " then "
+                      & Expr_Name (Then_Expr) & " else "
+                      & Expr_Name (Else_Expr);
                end;
 
             when N_Qualified_Expression =>