Find abi before trying to decode the stack.

The CallStack function prints stacks to the log. Unfortunately, our
stack script defaults to arm, so if the data is actually arm64, we'll
do nothing. Modify the script to parse the input trying to determine
the abi before processing the rest of the lines. At the very least,
we'll be able to correctly choose between arm and arm64.

The only downside, is that, the old method could take dumps from different
abis, but no one I know does this.

Bug: 26569638
Change-Id: I5935b82fe0af1e788b0d3edc535b9f0cbb7d1b28
3 files changed