Dimitry Andric:  Add const to constexpr member functions in order to cope with new C++1y language rules.  This silences -Wconstexpr-not-const warnings.

llvm-svn: 185181
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: afe8b967cc196bb276078bbc3fe6a8381b7ecfbe
diff --git a/include/chrono b/include/chrono
index 3b96e81..4ceb875 100644
--- a/include/chrono
+++ b/include/chrono
@@ -468,7 +468,7 @@
 struct __duration_eq
 {
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
-    bool operator()(const _LhsDuration& __lhs, const _RhsDuration& __rhs)
+    bool operator()(const _LhsDuration& __lhs, const _RhsDuration& __rhs) const
         {
             typedef typename common_type<_LhsDuration, _RhsDuration>::type _Ct;
             return _Ct(__lhs).count() == _Ct(__rhs).count();
@@ -479,7 +479,7 @@
 struct __duration_eq<_LhsDuration, _LhsDuration>
 {
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
-    bool operator()(const _LhsDuration& __lhs, const _LhsDuration& __rhs)
+    bool operator()(const _LhsDuration& __lhs, const _LhsDuration& __rhs) const
         {return __lhs.count() == __rhs.count();}
 };
 
@@ -509,7 +509,7 @@
 struct __duration_lt
 {
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
-    bool operator()(const _LhsDuration& __lhs, const _RhsDuration& __rhs)
+    bool operator()(const _LhsDuration& __lhs, const _RhsDuration& __rhs) const
         {
             typedef typename common_type<_LhsDuration, _RhsDuration>::type _Ct;
             return _Ct(__lhs).count() < _Ct(__rhs).count();
@@ -520,7 +520,7 @@
 struct __duration_lt<_LhsDuration, _LhsDuration>
 {
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
-    bool operator()(const _LhsDuration& __lhs, const _LhsDuration& __rhs)
+    bool operator()(const _LhsDuration& __lhs, const _LhsDuration& __rhs) const
         {return __lhs.count() < __rhs.count();}
 };