Roll SwiftShader from 34acfd537616 to c21aa26e0256 (2 revisions)

https://swiftshader.googlesource.com/SwiftShader.git/+log/34acfd537616..c21aa26e0256

2022-08-19 nicolas.capens@gmail.com Simplify clipping of complex polygons
2022-08-19 nicolas.capens@gmail.com Update Vulkan headers to version 1.3.225

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/swiftshader-dawn-autoroll
Please CC alanbaker@google.com on the revert to ensure that a human
is aware of the problem.

To file a bug in SwiftShader: https://bugs.chromium.org/p/swiftshader/issues/entry
To file a bug in Dawn: https://bugs.chromium.org/p/dawn/issues/entry

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/main/autoroll/README.md

Bug: None
Tbr: alanbaker@google.com
Change-Id: Ie4c51fcbfcdeb29f1dc3c28d653bf55a9474bec3
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/99840
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Dawn Autoroller <dawn-autoroll@skia-public.iam.gserviceaccount.com>
Bot-Commit: Dawn Autoroller <dawn-autoroll@skia-public.iam.gserviceaccount.com>

DEPS

@@ -134,7 +134,7 @@ deps = {
   },
 
   'third_party/swiftshader': {
-    'url': '{swiftshader_git}/SwiftShader@34acfd5376163529edbdbca85247fdbfa6ff5114',
+    'url': '{swiftshader_git}/SwiftShader@c21aa26e0256a3efed81740d6215acb393b61d9e',
     'condition': 'dawn_standalone',
   },