[libcxx] Add std::any

Summary:
This patch adds std::any by moving/adapting <experimental/any>.

This patch also implements the std::any parts of p0032r3 (http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0032r3.pdf)
and LWG 2509 (http://cplusplus.github.io/LWG/lwg-defects.html#2509).

I plan to push it in a day or two if there are no comments.


Reviewers: mclow.lists, EricWF

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D22733

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@278310 91177308-0d34-0410-b5e6-96231b3b80d8

test/libcxx/utilities/any/version.pass.cpp

@@ -0,0 +1,20 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+// <any>
+
+#include <any>
+
+#ifndef _LIBCPP_VERSION
+#error _LIBCPP_VERSION not defined
+#endif
+
+int main()
+{
+}