With this, `gclient` completes bootstrap after running

    echo "mac-arm64" > .cipd_client_platform

as long as you also run

    export VPYTHON_BYPASS="manually managed python not supported by chrome operations"

Things work enough that you can `fetch chromium`. You can then build
all of chrome (if you want to build all tests, you also need to
`echo "mac-arm64" > third_party/depot_tools/.cipd_client_platform`
in your chromium checkout).

Parts of depot_tools that actually need the env managed by vpython,
such as `git cl`, don't work. So you can't `git cl upload` for now.

Bug: 1184768,1103326,1184766,1184765,1103236
Change-Id: Ib559c35e9665b826db9841dd8a4fe0dea16f37ec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2807956
Auto-Submit: Nico Weber <thakis@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>
Reviewed-by: Vadim Shtayura <vadimsh@chromium.org>
Commit-Queue: Dirk Pranke <dpranke@google.com>