Vulkan: Skip VVL barrier warning on SwiftShader. This gets tripped up from our barrier handling code. Bug: angleproject:6656 Change-Id: Iefb1c898ca6506e81a19a0928beaf221dcdf8f4e Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3264225 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>