The problem is the -march=bpf option on the command line. Without it,
the code build, but is not a eBPF module. :(
Because of this, I had to exclude armhf from building the ebpf modules
in debian/rules. To test for yourself, update d/rules and add armhf to
the list of architectures with EBPF enabled.
The same code build with llvm-19 on arm64 and amd64.