This addresses a latency issue - chroot_fs_refs called inside pivot_root
in the kernel can take several milliseconds on machines with many threads
running.
This might not always reduce latency for custom forkservers, as additional
fork can be more costly than pivot_root.
PiperOrigin-RevId: 281306284
Change-Id: If503ac76a70e5438e94caf708d79cb0219c66def
Caused failures if root is mounted as nodev, nosuid etc.
Root is pivoted and unmounted right after this anyhow.
PiperOrigin-RevId: 273707731
Change-Id: I75f1edaf2877c096e4f5bb7dc1b2bb8eb5c437a3
