Attempt to fix tests on Windows

Author: simolus3

pkgs/native_toolchain_c/test/native_toolchain/ndk_test.dart

@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import 'dart:io';
+
 import 'package:native_toolchain_c/src/native_toolchain/android_ndk.dart';
 import 'package:native_toolchain_c/src/tool/tool_requirement.dart';
 import 'package:native_toolchain_c/src/tool/tool_resolver.dart';
@@ -39,7 +41,7 @@ void main() {
 
     expect(
       resolved.map((e) => e.uri.toFilePath()),
-      contains(d.path('fake_android/ndk/1.3.37/')),
+      contains(d.path('fake_android/ndk/1.3.37${Platform.pathSeparator}')),
     );
   });
 
@@ -58,7 +60,7 @@ void main() {
 
     expect(
       resolved.map((e) => e.uri.toFilePath()),
-      contains(d.path('weird/ndk/directory/')),
+      contains(d.path('weird/ndk/directory${Platform.pathSeparator}')),
     );
   });
 }