Roll libunwind from 0517d86d521b to edf77b2d2d22 (2 revisions)

https://chromium.googlesource.com/external/github.com/llvm/llvm-project/libunwind.git/+log/0517d86d521b..edf77b2d2d22

2021-09-02 hans@chromium.org [Unwind] Cast exception class pointer for strcpy
2021-09-02 daniel.kiss@arm.com [libunwind] Compile with -Wunused-but-set-variable

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

To file a bug in Chromium: https://bugs.chromium.org/p/chromium/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

Tbr: thakis@chromium.org,hans@chromium.org
Change-Id: I0965b18f100c819d03c3bdcba38911af1fc4d51f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3140323
Bot-Commit: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#917741}