Sync unwindlib option with current llvm

Use unwindlib=libunwind to match current production
wrapper.

BUG=None
TEST=go test

Change-Id: I6cdace48ed871ac87a093addf2b96b86ee5153c2
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/3621381
Reviewed-by: George Burgess <gbiv@chromium.org>
Tested-by: Manoj Gupta <manojgupta@chromium.org>
Commit-Queue: George Burgess <gbiv@chromium.org>
Auto-Submit: Manoj Gupta <manojgupta@chromium.org>
21 files changed