build/mac_toolchain.py was fixed for Python 3 in
https://crrev.com/c/2727724

Bug: angleproject:5707
Change-Id: I2f233157bedc3cc298250b8efc9bd68ac45cdc28
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2731707Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>