Add a test for uniqueptr having either NULL and nullptr

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@269665 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/utilities/memory/unique.ptr/unique.ptr.runtime/unique.ptr.runtime.ctor/pointer_deleter01.pass.cpp

@@ -40,4 +40,10 @@ int main()
     assert(s.get_deleter().state() == 0);
     }
     assert(A::count == 0);
+
+    { // LWG#2520 says that nullptr is a valid input as well as null
+    std::unique_ptr<A[], Deleter<A[]> > s1(NULL, Deleter<A[]>());
+    std::unique_ptr<A[], Deleter<A[]> > s2(nullptr, Deleter<A[]>());
+    }
+    assert(A::count == 0);
 }