Cleanup: Move mjsunit/regress-*.js into mjsunit/regress/.

test/mjsunit/regress/regress-4399.js

-// Copyright 2015 the V8 project authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-// Test that switch has the appropriate 'eval' value
-
-assertEquals("foo", eval('switch(1) { case 1: "foo" }'));
-assertEquals("foo", eval('{ switch(1) { case 1: "foo" } }'));
-assertEquals("foo", eval('switch(1) { case 1: { "foo" } }'));
-assertEquals("foo", eval('switch(1) { case 1: "foo"; break; case 2: "bar"; break }'));
-assertEquals("bar", eval('switch(2) { case 1: "foo"; break; case 2: "bar"; break }'));
-assertEquals("bar", eval('switch(1) { case 1: "foo"; case 2: "bar"; break }'));
-
-// The tag is not the value, if there's no value
-
-assertEquals(undefined, eval('switch (1) {}'));
-assertEquals(undefined, eval('switch (1) { case 1: {} }'));