win32: only count subdirectories if necessary

Commit 7fb95a2a5 (win32: try to get link count for directories)
allowed stat(2) to report accurate values of st_nlink for
directories.

There are only a couple of places in busybox-w32 where these values
are required.  Disable counting of subdirectories by default and
only enable it when necessary.

Microsoft kindly provide directories to test edge cases like this:

   C:/Windows/WinSxS           (contains many subdirectories)
   C:/Windows/WinSxS/Manifests (contains many files)

Adds 84-112 bytes.

1 files changed, 4 insertions, 0 deletions

diff --git a/coreutils/stat.c b/coreutils/stat.c
index 940ade89a..dc20c2356 100644
--- a/coreutils/stat.c
+++ b/coreutils/stat.c
@@ -785,6 +785,10 @@ int stat_main(int argc UNUSED_PARAM, char **argv)
                 selinux_or_die();
         }
 #endif
+#if ENABLE_FEATURE_EXTRA_FILE_DATA
+        /* Enable accurate link counts for directories */
+        count_subdirs(NULL);
+#endif
         ok = 1;
         argv += optind;
         for (i = 0; argv[i]; ++i)