More than a year ago (actually it's closer to two), this bug (https://bugbase.adobe.com/index.cfm?event=bug&id=3161034) (and a few duplicates) was filed. It has yet to be given a decent response.
I mean, sure, those CPUs are quite dated, but unless it's a high resolution video, flash worked quite decently there, so why did you have to gut it ? Espescially, that it seems to be a matter of a compiler switch.
PS: I don't really expect any decent response and this is a throw away account, but on the off chance, that you'll actually try fixing it, I'm giving it a try. Just about anything that needed to be said, already was in that bug.