Revert "Revert "Upgrade to 5.0.71.48"" DO NOT MERGE

This reverts commit f2e3994fa5148cc3d9946666f0b0596290192b0e,
and updates the x64 makefile properly so it doesn't break that
build.

FPIIM-449

Change-Id: Ib83e35bfbae6af627451c926a9650ec57c045605
(cherry picked from commit 109988c7ccb6f3fd1a58574fa3dfb88beaef6632)
diff --git a/test/mjsunit/es6/regexp-tostring.js b/test/mjsunit/es6/regexp-tostring.js
new file mode 100644
index 0000000..3deeeb7
--- /dev/null
+++ b/test/mjsunit/es6/regexp-tostring.js
@@ -0,0 +1,46 @@
+// Copyright 2016 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.
+
+var log = [];
+
+var fake =
+    {
+      get source() {
+        log.push("p");
+        return {
+          toString: function() {
+            log.push("ps");
+            return "pattern";
+          }
+        };
+      },
+      get flags() {
+        log.push("f");
+        return {
+          toString: function() {
+            log.push("fs");
+            return "flags";
+          }
+        };
+      }
+    }
+
+function testThrows(x) {
+  try {
+    RegExp.prototype.toString.call(x);
+  } catch (e) {
+    assertTrue(/incompatible receiver/.test(e.message));
+    return;
+  }
+  assertUnreachable();
+}
+
+testThrows(1);
+testThrows(null);
+Number.prototype.source = "a";
+Number.prototype.flags = "b";
+testThrows(1);
+
+assertEquals("/pattern/flags", RegExp.prototype.toString.call(fake));
+assertEquals(["p", "ps", "f", "fs"], log);