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_03 b/include/__functional_03
index e48bb68..5d30ce2 100644
--- a/include/__functional_03
+++ b/include/__functional_03
@@ -13,7 +13,9 @@
 
 // manual variadic expansion for <functional>
 
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
+#endif
 
 template <class _Tp>
 class __mem_fn