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

Summary:
This patch treats <filesystem> as a first-class citizen of the dylib,
like all other sub-libraries (e.g. <chrono>). As such, it also removes
all special handling for installing the filesystem library separately
or disabling part of the test suite from the lit command line.

Reviewers: mclow.lists, EricWF, serge-sans-paille

Subscribers: mgorny, christof, jkorous, dexonsmith, jfb, jdoerfert, libcxx-commits

Differential Revision: https://reviews.llvm.org/D59152

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@356500 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/input.output/filesystems/fs.enum/enum.path.format.pass.cpp

@@ -1,39 +0,0 @@
-//===----------------------------------------------------------------------===//
-//
-// 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;
-// enum class format;
-
-#include "filesystem_include.hpp"
-#include <type_traits>
-#include <cassert>
-
-#include "test_macros.h"
-
-int main(int, char**) {
-  typedef fs::path::format E;
-  static_assert(std::is_enum<E>::value, "");
-
-  // Check that E is a scoped enum by checking for conversions.
-  typedef std::underlying_type<E>::type UT;
-  static_assert(!std::is_convertible<E, UT>::value, "");
-
-  LIBCPP_ONLY(static_assert(std::is_same<UT, unsigned char>::value, "")); // Implementation detail
-
-  static_assert(
-          E::auto_format   != E::native_format &&
-          E::auto_format   != E::generic_format &&
-          E::native_format != E::generic_format,
-        "Expected enumeration values are not unique");
-
-  return 0;
-}