Roll engine 21b8224ae12d..1e58794b238b (2 commits) (#42287)

git@github.com:flutter/engine.git/compare/21b8224ae12d...1e58794b238b

git log 21b8224ae12d..1e58794b238b --no-merges --oneline
2019-10-09 chinmaygarde@gmail.com Revert "Upgrade compiler to Clang 10. (#11256)" (flutter/engine#13017)
2019-10-09 chinmaygarde@google.com Upgrade compiler to Clang 10. (flutter/engine#11256)


If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/flutter-engine-flutter-autoroll
Please CC chinmaygarde@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

bin/internal/engine.version

-21b8224ae12d94e00fc621d2a15160a0539c4b69
+1e58794b238b0c948f7208cf50bb139416de354f