Fix gclient-new-workdir when source repo is shallow clone
Fix gclient-new-workdir when source repo is shallow clone

When source repo is a 'shallow clone', `.git/shallow` is not linked to
the new workdir. Which makes running git command fails in new workdir.

Change-Id: I81d38b7b2cccc482711dcc1dd02ea06fbd01a56d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2211635
Reviewed-by: Aaron Gable <bbed39beedae4cdb499af742d2fcd6c63934d93b@chromium.org>
Commit-Queue: Richard He <075e67287f62c8542033afd2a9f63f80d591d370@microsoft.com>

CoherentLabs/depot_tools,CoherentLabs/depot_tools