[libcxx] Add <experimental/ratio>

Summary:
This patch is pretty simple. It just adds the _v traits from <ratio>. 

The draft can be found here.

Reviewers: jroelofs, K-ballo, mclow.lists

Reviewed By: mclow.lists

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D7351

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@229509 91177308-0d34-0410-b5e6-96231b3b80d8

include/experimental/ratio

@@ -0,0 +1,77 @@
+// -*- C++ -*-
+//===------------------------------ ratio ---------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP_EXPERIMENTAL_RATIO
+#define _LIBCPP_EXPERIMENTAL_RATIO
+
+/**
+    experimental/ratio synopsis
+    C++1y
+#include <ratio>
+
+namespace std {
+namespace experimental {
+inline namespace fundamentals_v1 {
+
+  // See C++14 20.11.5, ratio comparison
+  template <class R1, class R2> constexpr bool ratio_equal_v
+    = ratio_equal<R1, R2>::value;
+  template <class R1, class R2> constexpr bool ratio_not_equal_v
+    = ratio_not_equal<R1, R2>::value;
+  template <class R1, class R2> constexpr bool ratio_less_v
+    = ratio_less<R1, R2>::value;
+  template <class R1, class R2> constexpr bool ratio_less_equal_v
+    = ratio_less_equal<R1, R2>::value;
+  template <class R1, class R2> constexpr bool ratio_greater_v
+    = ratio_greater<R1, R2>::value;
+  template <class R1, class R2> constexpr bool ratio_greater_equal_v
+    = ratio_greater_equal<R1, R2>::value;
+
+} // namespace fundamentals_v1
+} // namespace experimental
+} // namespace std
+
+*/
+
+#include <experimental/__config>
+
+#if _LIBCPP_STD_VER > 11
+
+#include <ratio>
+
+_LIBCPP_BEGIN_NAMESPACE_LFTS
+
+#if __has_feature(cxx_variable_templates)
+
+template <class _R1, class _R2> _LIBCPP_CONSTEXPR bool ratio_equal_v
+    = ratio_equal<_R1, _R2>::value;
+
+template <class _R1, class _R2> _LIBCPP_CONSTEXPR bool ratio_not_equal_v
+    = ratio_not_equal<_R1, _R2>::value;
+
+template <class _R1, class _R2> _LIBCPP_CONSTEXPR bool ratio_less_v
+    = ratio_less<_R1, _R2>::value;
+
+template <class _R1, class _R2> _LIBCPP_CONSTEXPR bool ratio_less_equal_v
+    = ratio_less_equal<_R1, _R2>::value;
+
+template <class _R1, class _R2> _LIBCPP_CONSTEXPR bool ratio_greater_v
+    = ratio_greater<_R1, _R2>::value;
+
+template <class _R1, class _R2> _LIBCPP_CONSTEXPR bool ratio_greater_equal_v
+    = ratio_greater_equal<_R1, _R2>::value;
+
+#endif /* __has_feature(cxx_variable_templates) */
+
+_LIBCPP_END_NAMESPACE_LFTS
+
+#endif /* _LIBCPP_STD_VER > 11 */
+
+#endif _LIBCPP_EXPERIMENTAL_RATIO