Consolidate swap, swap_ranges, and iter_swap in <type_traits>.

NFC. Thanks to @Quuxplusone (Arthur O'Dwyer) for this change.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@371639 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/type_traits b/include/type_traits
index 657c0d5..03e8bba 100644
--- a/include/type_traits
+++ b/include/type_traits
@@ -3652,6 +3652,13 @@
 template <class _Tp> struct __is_swappable;
 template <class _Tp> struct __is_nothrow_swappable;
 
+// swap, swap_ranges
+
+template <class _ForwardIterator1, class _ForwardIterator2>
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
+_ForwardIterator2
+swap_ranges(_ForwardIterator1 __first1, _ForwardIterator1 __last1, _ForwardIterator2 __first2);
+
 template <class _Tp>
 inline _LIBCPP_INLINE_VISIBILITY
 #ifndef _LIBCPP_CXX03_LANG
@@ -3677,7 +3684,22 @@
 typename enable_if<
     __is_swappable<_Tp>::value
 >::type
-swap(_Tp (&__a)[_Np], _Tp (&__b)[_Np]) _NOEXCEPT_(__is_nothrow_swappable<_Tp>::value);
+swap(_Tp (&__a)[_Np], _Tp (&__b)[_Np]) _NOEXCEPT_(__is_nothrow_swappable<_Tp>::value)
+{
+    _VSTD::swap_ranges(__a, __a + _Np, __b);
+}
+
+template <class _ForwardIterator1, class _ForwardIterator2>
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
+_ForwardIterator2
+swap_ranges(_ForwardIterator1 __first1, _ForwardIterator1 __last1, _ForwardIterator2 __first2)
+{
+    for(; __first1 != __last1; ++__first1, (void) ++__first2)
+        swap(*__first1, *__first2);
+    return __first2;
+}
+
+// iter_swap
 
 template <class _ForwardIterator1, class _ForwardIterator2>
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
diff --git a/include/utility b/include/utility
index a185818..64599c8 100644
--- a/include/utility
+++ b/include/utility
@@ -248,29 +248,11 @@
 
 }  // rel_ops
 
-// swap_ranges
+// swap_ranges is defined in <type_traits>`
 
+// swap is defined in <type_traits>
 
-template <class _ForwardIterator1, class _ForwardIterator2>
-inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
-_ForwardIterator2
-swap_ranges(_ForwardIterator1 __first1, _ForwardIterator1 __last1, _ForwardIterator2 __first2)
-{
-    for(; __first1 != __last1; ++__first1, (void) ++__first2)
-        swap(*__first1, *__first2);
-    return __first2;
-}
-
-// forward declared in <type_traits>
-template<class _Tp, size_t _Np>
-inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
-typename enable_if<
-    __is_swappable<_Tp>::value
->::type
-swap(_Tp (&__a)[_Np], _Tp (&__b)[_Np]) _NOEXCEPT_(__is_nothrow_swappable<_Tp>::value)
-{
-    _VSTD::swap_ranges(__a, __a + _Np, __b);
-}
+// move_if_noexcept
 
 template <class _Tp>
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11