Add is_swappable/is_nothrow_swappable traits

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@267079 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/containers/sequences/array/array.swap/swap.pass.cpp

@@ -15,10 +15,19 @@
 #include <cassert>
 #include <array>
 
+#include "test_macros.h"
+
 // std::array is explicitly allowed to be initialized with A a = { init-list };.
 // Disable the missing braces warning for this reason.
 #include "disable_missing_braces_warning.h"
 
+struct NonSwappable {
+  NonSwappable() {}
+private:
+  NonSwappable(NonSwappable const&);
+  NonSwappable& operator=(NonSwappable const&);
+};
+
 int main()
 {
     {
@@ -70,5 +79,15 @@ int main()
         assert(c1.size() == 0);
         assert(c2.size() == 0);
     }
+    {
+        typedef NonSwappable T;
+        typedef std::array<T, 0> C0;
+        C0 l = {};
+        C0 r = {};
+        l.swap(r);
+#if TEST_STD_VER >= 11
+        static_assert(noexcept(l.swap(r)), "");
+#endif
+    }
 
 }