Make for_each_n only avaliable on C++17

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@303856 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/algorithm b/include/algorithm
index 168d2c4..a3bde9f 100644
--- a/include/algorithm
+++ b/include/algorithm
@@ -964,6 +964,7 @@
     return __f;
 }
 
+#if _LIBCPP_STD_VER > 14
 // for_each_n
 
 template <class _InputIterator, class _Size, class _Function>
@@ -981,6 +982,7 @@
     }
     return __first;
 }
+#endif
 
 // find
 
@@ -1758,7 +1760,7 @@
 }
 
 template <class _Tp>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
 typename enable_if
 <
     is_trivially_copy_assignable<_Tp>::value,
@@ -1772,7 +1774,7 @@
 #if _LIBCPP_DEBUG_LEVEL < 2
 
 template <class _Tp>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
 typename enable_if
 <
     is_trivially_copy_assignable<_Tp>::value,
@@ -1786,7 +1788,7 @@
 #else
 
 template <class _Tp>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
 typename enable_if
 <
     is_trivially_copy_assignable<_Tp>::value,