[libbacktrace] Modernize code to use override keyword

Generated by clang-tidy.

Test: m checkbuild
Change-Id: I4506a9624002250117148413ea6990749cc1a4da
1 file changed
tree: 6ac0e533632c481117fd10bb94fe8e647242aed8
  1. libbacktrace/
  2. libunwindstack/