[libc++][NFC] Remove uses of 'using namespace std;' in the test suite

Differential Revision: https://reviews.llvm.org/D109120

libcxx/test/std/strings/string.view/string_view.literals/literal.verify.cpp

@@ -0,0 +1,22 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11
+
+#include <string_view>
+
+void f() {
+  {
+    using std::string_view;
+    string_view foo = ""sv; // expected-error {{no matching literal operator}}
+  }
+  {
+    std::string_view foo = ""sv; // expected-error {{no matching literal operator}}
+  }
+}