split Exit and Die nodes

php7/php7.y

@@ -1844,7 +1844,11 @@ expr_without_variable:
         }
     |   T_EXIT exit_expr
         {
-            $$ = expr.NewExit($2, strings.EqualFold($1.Value, "die"))
+            if (strings.EqualFold($1.Value, "die")) {
+                $$ = expr.NewDie($2)
+            } else {
+                $$ = expr.NewExit($2)
+            }
             positions.AddPosition($$, positionBuilder.NewTokenNodePosition($1, $2))
             comments.AddComments($$, $1.Comments())
         }

php7/php7_test.go

@@ -2206,25 +2206,19 @@ CAD;
 				},
 			},
 			&stmt.Expression{
-				Expr: &expr.Exit{
-					IsDie: false,
-				},
+				Expr: &expr.Exit{},
 			},
 			&stmt.Expression{
 				Expr: &expr.Exit{
-					IsDie: false,
-					Expr:  &expr.Variable{VarName: &node.Identifier{Value: "$a"}},
+					Expr: &expr.Variable{VarName: &node.Identifier{Value: "$a"}},
 				},
 			},
 			&stmt.Expression{
-				Expr: &expr.Exit{
-					IsDie: true,
-				},
+				Expr: &expr.Die{},
 			},
 			&stmt.Expression{
-				Expr: &expr.Exit{
-					IsDie: true,
-					Expr:  &expr.Variable{VarName: &node.Identifier{Value: "$a"}},
+				Expr: &expr.Die{
+					Expr: &expr.Variable{VarName: &node.Identifier{Value: "$a"}},
 				},
 			},
 			&stmt.Expression{