Hello. Thanks for taking care of this.
I'd like to emphasize that this is most probably a Makefile bug (or whatever is the proper name when using cmake), maybe a missing dependency somewhere. I discovered it by building all packages in bullseye using virtual machines with a single CPU, and the fact that the build seems to work with 2 CPUs is what makes me think that it's a Makefile bug. If you need to reproduce it, you can use GRUB_CMDLINE_LINUX="nr_cpus=1" in /etc/default/grub and most probably the build failure will happen. (And, in case it would not, my offer to provide a virtual machine where it happens still holds). Thanks.
