Experimental support for a meaningful __is_swappable<T>::value.  This does not appear to be strictly needed for correct functioning of the library.  If it causes any problems, I'd rather pull it sooner rather than later.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@132421 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/array b/include/array
index 188d24d..888fac2 100644
--- a/include/array
+++ b/include/array
@@ -270,7 +270,11 @@
 
 template <class _Tp, size_t _Size>
 _LIBCPP_INLINE_VISIBILITY inline
-void
+typename enable_if
+<
+    __is_swappable<_Tp>::value,
+    void
+>::type
 swap(const array<_Tp, _Size>& __x, const array<_Tp, _Size>& __y)
                                   _NOEXCEPT_(__is_nothrow_swappable<_Tp>::value)
 {