At the time when we discussed this, we argued that the only hope was
with dwarf2 CFI, but it just so happens that I noticed the exact same
sort of problem on Windows XP (where we don't have dwarf-2 :-/).
I have been brooding for a while over this, and really don't see any
solution to this, right now. Maybe it's unfair to say this: I find
the new frame code well structured and blissfully free of all the hacks
we used to have. However, it seems less tolerant to difficult cases,
where we just stop unwinding while we used to be able to have a useful
backtrace with 5.3.
(please don't see this as a complaint or don't think I am pointing
finger at anybody - if I had found a better solution, believe me,
I would have sent a suggestion).