More windows port work by Ruben Van Boxem

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@142732 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/string b/include/string
index 4e29e8a..5f5a347 100644
--- a/include/string
+++ b/include/string
@@ -1023,7 +1023,14 @@
 #endif
 }
 
+#ifdef _MSC_VER
+#pragma warning( push )
+#pragma warning( disable: 4231 )
+#endif // _MSC_VER
 extern template class __basic_string_common<true>;
+#ifdef _MSC_VER
+#pragma warning( pop )
+#endif // _MSC_VER
 
 template<class _CharT, class _Traits, class _Allocator>
 class _LIBCPP_VISIBLE basic_string