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/__tree b/include/__tree
index 6c4b6e6..ad5d2f4 100644
--- a/include/__tree
+++ b/include/__tree
@@ -17,7 +17,9 @@
 #include <stdexcept>
 #include <algorithm>
 
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
+#endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD