[regexp] Fix passing all flags to RegExp construction

test/mjsunit/harmony/regexp-dotall.js

 // Copyright 2017 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.
 
 // Flags: --harmony-regexp-dotall
 
 function toSlowMode(re) {
   re.exec = (str) => RegExp.prototype.exec.call(re, str);
   return re;
 }
@@ skipping 38 matching lines @@
   re = /./gimyu;
   assertEquals("gimuy", re.flags);
   assertTrue(re.global);
   assertTrue(re.ignoreCase);
   assertTrue(re.multiline);
   assertTrue(re.sticky);
   assertTrue(re.unicode);
   assertFalse(re.dotAll);
 }
 
+// Different construction variants with all flags.
+{
+  assertEquals("gimsuy", new RegExp("", "yusmig").flags);
+  assertEquals("gimsuy", new RegExp().compile("", "yusmig").flags);
+}
+
 // Default '.' behavior.
 {
   let re = /^.$/;
   assertTrue(re.test("a"));
   assertTrue(re.test("3"));
   assertTrue(re.test("π"));
   assertTrue(re.test("\u2027"));
   assertTrue(re.test("\u0085"));
   assertTrue(re.test("\v"));
   assertTrue(re.test("\f"));
@@ skipping 51 matching lines @@
   assertTrue(re.test("\u0085"));
   assertTrue(re.test("\v"));
   assertTrue(re.test("\f"));
   assertTrue(re.test("\u180E"));
   assertTrue(re.test("\u{10300}"));  // Supplementary plane.
   assertTrue(re.test("\n"));
   assertTrue(re.test("\r"));
   assertTrue(re.test("\u2028"));
   assertTrue(re.test("\u2029"));
 }