Add support for CFI based stack walking on Arm64.

This CL adds CFI based stack walking support for Arm64 to BreakPad along with
unit tests.  The Arm64 CFI stack walker is based on the Arm CFI stack walker

BUG=367367,335641,354405
R=blundell@chromium.org, mark@chromium.org

Review URL: https://breakpad.appspot.com/1664002

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1325 4c0a9323-5329-0410-9bdc-e9ce6186880e
FD leaks and handle errors better.

Patch from Matthew Dempsky <mdempsky@chromium.org>.
Original review: https://breakpad.appspot.com/5654002/

Review URL: https://breakpad.appspot.com/1674002

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1326 4c0a9323-5329-0410-9bdc-e9ce6186880e