Even though they shouldn't matter for color attachment, but Qualcomm's
performance validation layer is producing tons of this warning message.
This basically always set to DontCare even for color attachment.

Bug: b/158708100
Change-Id: Iaba39e099c9cc4716548f337ded74fa5f29bb654
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2240498
Commit-Queue: Charlie Lao <cclao@google.com>
Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>