[libc++] Fix unknown pragma warning on MSVC

llvm-svn: 299942
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 3f5b5fff8a831136d9f56eb67d00667f0f45f23f
diff --git a/include/limits b/include/limits
index b15f8f1..609c4d4 100644
--- a/include/limits
+++ b/include/limits
@@ -101,12 +101,12 @@
 }  // std
 
 */
+#include <__config>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
 #endif
 
-#include <__config>
 #include <type_traits>
 
 #include <__undef_min_max>