Fix windows build of new source accessor test

We don't have the dirFd on window at this time.

src/libutil-tests/source-accessor.cc

@@ -91,7 +91,9 @@ TEST_F(FSSourceAccessorTest, works)
     {
         RestoreSink sink(false);
         sink.dstPath = tmpDir;
+#ifndef _WIN32
         sink.dirFd = openDirectory(tmpDir);
+#endif
         sink.createDirectory(CanonPath("subdir"));
         sink.createRegularFile(CanonPath("file1"), [](CreateRegularFileSink & crf) { crf("content1"); });
         sink.createRegularFile(CanonPath("subdir/file2"), [](CreateRegularFileSink & crf) { crf("content2"); });