Roll SPIRV-Tools from c2b2b5788575 to a61d07a72763 (3 revisions)

https://chromium.googlesource.com/external/github.com/KhronosGroup/SPIRV-Tools.git/+log/c2b2b5788575..a61d07a72763

2020-11-05 46493288+sfricke-samsung@users.noreply.github.com spirv-val: Fix SPV_KHR_fragment_shading_rate VUID label (#4014)
2020-11-05 46493288+sfricke-samsung@users.noreply.github.com spirv-val: Label Layer and ViewportIndex VUIDs (#4013)
2020-11-05 alanbaker@google.com Add dead function elimination to -O (#4015)

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/spirv-tools-chromium-autoroll
Please CC radial-bots+chrome-roll@google.com,courtneygo@google.com on the revert to ensure that a human
is aware of the problem.

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+doc/master/autoroll/README.md

Cq-Include-Trybots: luci.chromium.try:android_angle_vk32_deqp_rel_ng;luci.chromium.try:android_angle_vk32_rel_ng;luci.chromium.try:android_angle_vk64_deqp_rel_ng;luci.chromium.try:android_angle_vk64_rel_ng;luci.chromium.try:linux_angle_deqp_rel_ng;luci.chromium.try:linux-angle-rel;luci.chromium.try:win-angle-rel-32;luci.chromium.try:win-angle-rel-64;luci.chromium.try:win-angle-deqp-rel-32;luci.chromium.try:win-angle-deqp-rel-64
Tbr: radial-bots+chrome-roll@google.com,courtneygo@google.com
Change-Id: Ic15c1ac4475321f5f2becc834cf77370ed9a5d0e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2523015


Reviewed-by: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Commit-Queue: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#824790}