Use #pragma once header guard. am: 0cd3943fb8 am: a9b336ef84 am: b2c0842e51 am: 5458702d07

Original change: https://android-review.googlesource.com/c/platform/system/unwinding/+/2070169

Change-Id: I6d49f2c6e9998738a69a88d899b7aed7c482e726
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>
tree: d7791735cd60241ffb1584d4e6843cd6c86a34a0
  1. libbacktrace/
  2. libunwindstack/
  3. OWNERS
  4. PREUPLOAD.cfg