Windows support by Ruben Van Boxem.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@142235 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/functional b/include/functional
index 6db7ac4..59b132c 100644
--- a/include/functional
+++ b/include/functional
@@ -467,7 +467,9 @@
 
 #include <__functional_base>
 
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
+#endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD