libc++fs is part of libc++ now. am: d3c93ed418

Original change: https://android-review.googlesource.com/c/device/google/barbet/+/3118834

Change-Id: If0cb5c805b1cff54f83cb1a0489340af72a89ddc
Signed-off-by: Automerger Merge Worker <[email protected]>