Revert "[libc++] Build <filesystem> support as part of the dylib"

When I applied r356500 (https://reviews.llvm.org/D59152), I somehow
deleted all of filesystem's tests. I will revert r356500 and re-apply
it properly.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@356505 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/input.output/filesystems/class.path/path.member/path.construct/default.pass.cpp

@@ -0,0 +1,31 @@
+//===----------------------------------------------------------------------===//
+//
+// 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++98, c++03
+
+// <filesystem>
+
+// class path
+
+// path() noexcept
+
+#include "filesystem_include.hpp"
+#include <type_traits>
+#include <cassert>
+
+#include "test_macros.h"
+
+
+int main(int, char**) {
+  using namespace fs;
+  static_assert(std::is_nothrow_default_constructible<path>::value, "");
+  const path p;
+  assert(p.empty());
+
+  return 0;
+}