Add protection from min/max macros

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@145407 91177308-0d34-0410-b5e6-96231b3b80d8

include/ratio

@@ -70,6 +70,8 @@ typedef ratio<1000000000000000000000000, 1> yotta;  // not supported
 #include <climits>
 #include <type_traits>
 
+#include <__undef_min_max>
+
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
 #endif