The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/chromite/+/37b43b891b865c1255414829f84dd1f2093411d0

commit 37b43b891b865c1255414829f84dd1f2093411d0
Author: Manoj Gupta <manojgupta@google.com>
Date: Thu Jul 20 07:37:02 2017

Stop building llvm-libwind as part of cross-packages.

There is no current user of llvm-libunwind.
Drop it from cross packages list to avoid any confusion
about unwinder library in SDK.

BUG= chromium:746571 
TEST=llvm-libunwind does not get built when running cros_setup_toolchains.

Change-Id: I5e4ccc56814d4531299d791dd34ca90ffd09b03b
Reviewed-on: https://chromium-review.googlesource.com/578467
Commit-Ready: Manoj Gupta <manojgupta@chromium.org>
Tested-by: Manoj Gupta <manojgupta@chromium.org>
Reviewed-by: Yunlian Jiang <yunlian@chromium.org>

[modify] https://crrev.com/37b43b891b865c1255414829f84dd1f2093411d0/scripts/cros_setup_toolchains.py