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.

llvm-svn: 356505
diff --git a/libcxx/test/std/input.output/filesystems/class.path/synop.pass.cpp b/libcxx/test/std/input.output/filesystems/class.path/synop.pass.cpp
new file mode 100644
index 0000000..8aa186e
--- /dev/null
+++ b/libcxx/test/std/input.output/filesystems/class.path/synop.pass.cpp
@@ -0,0 +1,39 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+
+// typedef ... value_type;
+// typedef basic_string<value_type> string_type;
+// static constexpr value_type preferred_separator = ...;
+
+#include "filesystem_include.hpp"
+#include <type_traits>
+#include <cassert>
+
+#include "test_macros.h"
+
+
+int main(int, char**) {
+  using namespace fs;
+  ASSERT_SAME_TYPE(path::value_type, char);
+  ASSERT_SAME_TYPE(path::string_type, std::basic_string<path::value_type>);
+  {
+    ASSERT_SAME_TYPE(const path::value_type, decltype(path::preferred_separator));
+    static_assert(path::preferred_separator == '/', "");
+    // Make preferred_separator ODR used by taking its address.
+    const char* dummy = &path::preferred_separator;
+    ((void)dummy);
+  }
+
+  return 0;
+}