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/iosfwd b/include/iosfwd
index 7e5ac73..efdff5f 100644
--- a/include/iosfwd
+++ b/include/iosfwd
@@ -95,7 +95,7 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-class ios_base;
+class _LIBCPP_VISIBLE ios_base;
 
 template<class _CharT>  struct _LIBCPP_VISIBLE char_traits;
 template<class _Tp>     class _LIBCPP_VISIBLE allocator;