visibility-decoration.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@114486 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/cstddef b/include/cstddef
index a5297ec..def48bc 100644
--- a/include/cstddef
+++ b/include/cstddef
@@ -54,7 +54,7 @@
 
 #ifdef _LIBCPP_HAS_NO_NULLPTR
 
-struct nullptr_t
+struct _LIBCPP_VISIBLE nullptr_t
 {
     void* _;