Greetings. I can reproduce this bug, and I've put a bunch of failed build logs here:
https://people.debian.org/~sanvila/build-logs/hkl/ The bug happens "randomly", but in a very particular way: always in some instances and never in the others. I believe this may be some sort of Makefile bug which is related to filesystem ordering or something similar, but I don't really know. In either case, I could easily offer ssh access to a machine where this happens to anybody interested in debugging the problem (please contact me privately for details). While we are at it: I'm still doing QA for buster, so I'd appreciate (once we find a fix) if we could fix this in buster as well (it's a FTBFS bug after all). I would be willing to help if required, either by preparing an upload for stable, filing a release.debian.org bug, or both. Thanks.