[SRU xenial/artful V2] LP#1751021 -- i386 retpoline trackers not populated

[Andy Whitcroft]

We are not correctly extracting the retpoline tracker information on
i386 leading to those being empty and thus would always pass.

Fix the extractor so to handle the different mnemonics used in 32bit mode.
Also add a checker which fires at insertchanges time to check the whole
of the ABI.  For each required element check it is present or correctly
ignored.  Finally add a specific check for the present but empty
retpoline file and report those.

Proposing for SRU to xenial and artful.

-apw