add a -Wuffs bot

Change-Id: Idec98e922e81e062b78403bb83473e20a49dd13e
Reviewed-on: https://skia-review.googlesource.com/c/191292
Auto-Submit: Mike Klein <mtklein@google.com>
Commit-Queue: Leon Scroggins <scroggo@google.com>
Reviewed-by: Leon Scroggins <scroggo@google.com>
5 files changed