[libcxx] [test] Split the file_time_type synopsis test

Split the resolution check to a separate test, which is marked as
unsupported on windows.

On windows (both with MS STL and libstdc++), the file time has
100 ns resolution; the standard doesn't mandate a specific resolution.

Differential Revision: https://reviews.llvm.org/D89535

libcxx/test/std/input.output/filesystems/fs.filesystem.synopsis/file_time_type.pass.cpp

@@ -32,16 +32,8 @@ void test_trivial_clock() {
   ((void)odr_use);
 }
 
-void test_time_point_resolution_and_range() {
-  using namespace fs;
-  using Dur = file_time_type::duration;
-  using Period = Dur::period;
-  ASSERT_SAME_TYPE(Period, std::nano);
-}
-
 int main(int, char**) {
   test_trivial_clock();
-  test_time_point_resolution_and_range();
 
   return 0;
 }

libcxx/test/std/input.output/filesystems/fs.filesystem.synopsis/file_time_type_resolution.compile.pass.cpp

@@ -0,0 +1,27 @@
+//===----------------------------------------------------------------------===//
+//
+// 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, windows
+
+// MS STL and libstdc++ use the native windows file timestamp resolution,
+// with 100 ns resolution.
+
+// <filesystem>
+
+// typedef TrivialClock file_time_type;
+
+#include "filesystem_include.h"
+#include <chrono>
+#include <type_traits>
+
+#include "test_macros.h"
+
+using namespace fs;
+using Dur = file_time_type::duration;
+using Period = Dur::period;
+ASSERT_SAME_TYPE(Period, std::nano);