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/exception b/include/exception
index 2f527d9..5b75fb0 100644
--- a/include/exception
+++ b/include/exception
@@ -116,7 +116,7 @@
 
 _LIBCPP_VISIBLE bool uncaught_exception() _NOEXCEPT;
 
-class exception_ptr;
+class _LIBCPP_VISIBLE exception_ptr;
 
 exception_ptr current_exception() _NOEXCEPT;
 _LIBCPP_NORETURN void rethrow_exception(exception_ptr);