I am experimenting with putting visibility-default attributes on all struct/classes in libc++.  This checkin decorates only basic_string and vector as an experiment, and for review by those in this audience that might know more about visibilty than I do.  If I get no negative feedback on this procedure I will begin to decorate the entire library in this way.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@113590 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/memory b/include/memory
index 5b2b41d..b4875ce 100644
--- a/include/memory
+++ b/include/memory
@@ -1471,7 +1471,7 @@
 // allocator
 
 template <class _Tp>
-class allocator
+class _LIBCPP_VISIBLE allocator
 {
 public:
     typedef size_t            size_type;