Roll SPIRV-Tools from 34ef0c3fdc8e to 50ae4c5f4427 (3 revisions)

https://chromium.googlesource.com/external/github.com/KhronosGroup/SPIRV-Tools.git/+log/34ef0c3fdc8e..50ae4c5f4427

2020-09-18 afdx@google.com Fix header guard macros (#3811)
2020-09-18 antonikarp@google.com spirv-fuzz: Fix TransformationDuplicateRegionWithSelection (#3815)
2020-09-17 46493288+sfricke-samsung@users.noreply.github.com spirv-val: Add DeviceIndex (#3812)

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,jmadill@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,jmadill@google.com
Change-Id: I06be9bb43a2a9d22736c7ea1d263cf0b8e99605f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2417079Reviewed-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@{#808292}

DEPS

@@ -302,7 +302,7 @@ vars = {
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling feed
   # and whatever else without interference from each other.
-  'spv_tools_revision': '34ef0c3fdc8e235fd6217a64c824b6ceac93be60',
+  'spv_tools_revision': '50ae4c5f4427381a0be8a408d908fc753d815ad8',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling feed
   # and whatever else without interference from each other.