All warranties disclaimed 
These were built over the last couple of days, on a Debian system running a relatively up-to date unstable, but the dependencies aren’t too onerous, so I think they should run on any reasonably up to date Debian.
Basically, I backported the released Exiv2 v0.27.4, and built is with ISOBMFF support, then checked out git master for darktable a few hours ago, replaced the rawspeed lib with the canon_cr3 branch from cytrinox’s repo, and rebuilt that using the debian packaging from 3.6.1.
It works for me - hopefully these packages might help some other folks. I’ve uploaded all the debs I built, but I think the only ones you’ll actually need are libexiv and darktable (and the exiv2 one if you want the exiv2 cli tools). Uploaded to mega using a free account. Hope they save someone some time.