Roll SwiftShader c8403ec..cbb80f5

https://swiftshader.googlesource.com/SwiftShader.git/+log/c8403ec..cbb80f5

BUG=chromium:835299,chromium:825545

TBR=kbr@chromium.org

TEST=bots

CQ_INCLUDE_TRYBOTS=luci.chromium.try:win_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_chromium_cfi_rel_ng;luci.chromium.try:android_optional_gpu_tests_rel

Change-Id: Ic37afa51eaa67f7a61902d2a3e2d8227065ae909
Reviewed-on: https://chromium-review.googlesource.com/1066397
Reviewed-by: Alexis Hétu <sugoi@chromium.org>
Commit-Queue: Nicolas Capens <capn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#560042}