Roll SwiftShader from 669d12d7f034 to 4db20a80409b (2 revisions)

https://swiftshader.googlesource.com/SwiftShader.git/+log/669d12d7f034..4db20a80409b

2022-01-28 srisser@google.com Regres queries gerrit with a CL's numeric ID
2022-01-28 tho.laroche@gmail.com Check shm extension is supported before using it

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 bajones@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: bajones@google.com
Change-Id: I40e90b1955858400a7f3fa3739f5af301f5ef487
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/78682
Bot-Commit: Dawn Autoroller <dawn-autoroll@skia-public.iam.gserviceaccount.com>
Commit-Queue: Dawn Autoroller <dawn-autoroll@skia-public.iam.gserviceaccount.com>
diff --git a/DEPS b/DEPS
index 99110a3..a6d48fc 100644
--- a/DEPS
+++ b/DEPS
@@ -133,7 +133,7 @@
   },
 
   'third_party/swiftshader': {
-    'url': '{swiftshader_git}/SwiftShader@669d12d7f034bb7fe04b45228dbe7ca7c2f1c586',
+    'url': '{swiftshader_git}/SwiftShader@4db20a80409b207b3e134c93968468b7c3783eb6',
     'condition': 'dawn_standalone',
   },