[libcxx] [test] Portability fix: change header for struct hash.

[amakc11]

Summary

The Emplaceble.h test header defines hash function for containers used during testing. For this purpose, it creates a specialization of struct hash template defined in namespace std. However, to get access to struct hash it includes wrong header <utility>. According to C++11 standard, struct hash should be defined in the following standard headers:

1. <system_error> (section [syserr]);
2. <bitset> (section [template.bitset]);
3. <memory> (section [memory.syn]);
4. <functional> (sections [function.objects], [unord.hash]);
5. <typeindex> (section [type.index.synopsis]);
6. <string> (section [string.classes]);
7. <vector> (section [sequences.general]);
8. <thread> (section [thread.thread.id]).

Header <utility> is not in this list even in the later editions of the standard. As a result, tests including Emplaceble.h test header won't compile against some conformant libraries. The choice for <functional> as a substitute is made in accordance with the recommendation to applications.

[ldionne]

Committed as r347233. Thanks.

test/std/containers/Emplaceable.h

 //===----------------------------------------------------------------------===//
 //
 //                     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.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef EMPLACEABLE_H
 #define EMPLACEABLE_H
 
-#include <utility>
+#include <functional>
 #include "test_macros.h"
 
 #if TEST_STD_VER >= 11
 
 class Emplaceable
 {
     Emplaceable(const Emplaceable&);
     Emplaceable& operator=(const Emplaceable&);