abort if JIT triggered when AVIAN_AOT_ONLY is defined

If AVIAN_AOT_ONLY is defined and the VM is asked to compile a method
anyway, we should abort immediately rather than let it crash later
(e.g. due to an access violation on a non-jailbroken iPhone).  This
makes debugging such issues a bit easier since the failure will come
earlier and with a more obvious cause.
Merge pull request #339 from dicej/aotonly

abort if JIT triggered when AVIAN_AOT_ONLY is defined