Roll src/third_party/swiftshader 540bdf92531d..8cef397d7dec (3 commits)

https://swiftshader.googlesource.com/SwiftShader.git/+log/540bdf92531d..8cef397d7dec

git log 540bdf92531d..8cef397d7dec --date=short --first-parent --format='%ad %ae %s'
2020-03-25 bclayton@google.com CMake: Don't export LLVM_INCLUDE_DIR to PARENT_SCOPE
2020-03-25 bclayton@google.com CMake: Move LLVM rules out to third_party/llvm-7.0
2020-03-25 bclayton@google.com Add missing copyright header to CMakeLists.txt

Created with:
  gclient setdep -r src/third_party/swiftshader@8cef397d7dec

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/swiftshader-chromium-autoroll
Please CC swiftshader-team+autoroll@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/+/master/autoroll/README.md

Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_chromium_msan_rel_ng;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Bug: None
Tbr: swiftshader-team+autoroll@google.com
Change-Id: I3504ce618e05eaa4c9bc9904ae74001e18259b56
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2120901Reviewed-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@{#753333}

DEPS

@@ -191,7 +191,7 @@ vars = {
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling SwiftShader
   # and whatever else without interference from each other.
-  'swiftshader_revision': '540bdf92531d0c325d7b5c770ec33e869b56059f',
+  'swiftshader_revision': '8cef397d7dec8a8d4c5c7ab257655dc093e3bfa5',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling PDFium
   # and whatever else without interference from each other.