add Windows -Wuffs builders

Should help us figure out the build warnings and errors.

I figure we probably don't need any more than the existing one Linux
test bot until we're looking to make the big switch?

Bug: skia:8764
Change-Id: I7a8b427e3ac7278907e67f140d9e067161cd2123
Reviewed-on: https://skia-review.googlesource.com/c/192027
Reviewed-by: Leon Scroggins <scroggo@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
2 files changed