Add win_clang to CQ trybots. BUG=angleproject:1311 Change-Id: I5a9f381ef7e7e18b20919f791beb2be7f2ddd7a5 Reviewed-on: https://chromium-review.googlesource.com/361064 Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>