build_abi.sh: also check for the existence of abidiff

Before we were only checking whether the correct version of abidiff was
in PATH. In case there was no abidiff at all, we failed rather loud with
a lot of noise from dpkg. Hence do a quick check for abidiff before
comparing versions.

Change-Id: I056a292556fb519b8ca6880746ee034528750724
Signed-off-by: Matthias Maennich <maennich@google.com>
1 file changed