shflags: move to chromiumos-overlay

We need to apply some patches from upstream to address the following
issue:

https://github.com/kward/shflags/issues/50

BUG=b:247120346
TEST=use patched shflags on octopus, nesting shell programs which both
use shflags

Cq-Depend: chromium:3905629
Change-Id: Iab14b4125bbeea8276c6457edc76a3cd01aa4f7f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/portage-stable/+/3906002
Tested-by: Ross Zwisler <zwisler@google.com>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Commit-Queue: Ross Zwisler <zwisler@google.com>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Auto-Submit: Ross Zwisler <zwisler@google.com>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
3 files changed