Add mac_xcode_version gclient arg to DEPS
Add mac_xcode_version gclient arg to DEPS

Chromium's //build/ requires the DEPS file to produce gclient_args.gni
that contains a mac_xcode_version variable

Bug: angleproject:4878
Change-Id: I24421173347e1b508913d49793a065ccd52a47e7
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2321395
Commit-Queue: Jonah Ryan-Davis <682bdb9e7d8ba359ef169b8db374e7a99d394a46@google.com>
Reviewed-by: Corentin Wallez <470c533e86f4f848c98c7e11fffc2d043494a401@chromium.org>
Reviewed-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>

ppy/angle,ppy/angle,ppy/angle,ppy/angle