restore emplacement syntax (obsolete)

src/libsyntax/fold.rs

@@ -1194,6 +1194,9 @@ pub fn noop_fold_expr<T: Folder>(Expr {id, node, span, attrs}: Expr, folder: &mu
             ExprKind::Box(e) => {
                 ExprKind::Box(folder.fold_expr(e))
             }
+            ExprKind::ObsoleteInPlace(a, b) => {
+                ExprKind::ObsoleteInPlace(folder.fold_expr(a), folder.fold_expr(b))
+            }
             ExprKind::Array(exprs) => {
                 ExprKind::Array(folder.fold_exprs(exprs))
             }