Some versions of bash for windows report their uname -s as "MSYS_NT-10.0-{VERSION}",
this updates the wrapper script to handle them.

Change-Id: I5916324fc93d86d71f97ae3ad8497a5bb11a350c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1941341
Auto-Submit: Samuel Attard <samuel.r.attard@gmail.com>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>