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/utility b/include/utility
index a0e16a7..df693ec 100644
--- a/include/utility
+++ b/include/utility
@@ -419,7 +419,7 @@
 
 #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
 
-template <class _Tp> class reference_wrapper;
+template <class _Tp> class _LIBCPP_VISIBLE reference_wrapper;
 
 template <class _Tp>
 struct ___make_pair_return