Revert "Revert "Update aosp/master libcxx rebase to r263688""

This reverts commit 1d4a1edbc7.

Change-Id: I2909937fe582f2c5552bc86e7f4d2d5cff0de0aa

test/libcxx/extensions/hash/specializations.fail.cpp

@@ -0,0 +1,17 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include <assert.h>
+#include <ext/hash_map>
+#include <string>
+
+int main()
+{
+    assert(__gnu_cxx::hash<std::string>()(std::string()) == 0);  // error
+}