[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

llvm-svn: 278310
diff --git a/libcxx/src/any.cpp b/libcxx/src/any.cpp
index f776845..45b2337 100644
--- a/libcxx/src/any.cpp
+++ b/libcxx/src/any.cpp
@@ -7,12 +7,17 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "any"
 #include "experimental/any"
 
-_LIBCPP_BEGIN_NAMESPACE_LFTS
-
+namespace std {
 const char* bad_any_cast::what() const _NOEXCEPT {
     return "bad any cast";
 }
+}
 
+_LIBCPP_BEGIN_NAMESPACE_LFTS
+const char* bad_any_cast::what() const _NOEXCEPT {
+    return "bad any cast";
+}
 _LIBCPP_END_NAMESPACE_LFTS