Dimitry Andric:  many visibility fixes.  Howard:  Much appreciated.  Can you send me a patch to CREDITS.TXT?

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@163862 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/tuple b/include/tuple
index d2bc21f..65af3eb 100644
--- a/include/tuple
+++ b/include/tuple
@@ -803,7 +803,7 @@
 
 namespace { const __ignore_t<unsigned char> ignore = __ignore_t<unsigned char>(); }
 
-template <class _Tp> class reference_wrapper;
+template <class _Tp> class _LIBCPP_VISIBLE reference_wrapper;
 
 template <class _Tp>
 struct ___make_tuple_return