Add <variant> tests but disable them for libc++

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@287728 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/utilities/variant/variant.synopsis/variant_npos.pass.cpp

@@ -0,0 +1,21 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+
+// <variant>
+
+// constexpr size_t variant_npos = -1;
+
+#include <variant>
+
+int main() {
+  static_assert(std::variant_npos == static_cast<std::size_t>(-1), "");
+}