`failed to configure kernel: unsupported architecture` when following README

[pchaigno]

$ uname -a
Linux Mem 6.8.0-55-generic #57-Ubuntu SMP PREEMPT_DYNAMIC Wed Feb 12 23:42:21 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux
$ go run ./cmd/lvh kernels --dir _data init
$ go run ./cmd/lvh kernels --dir _data add ipsec-next git://git.kernel.org/pub/scm/linux/kernel/git/klassert/ipsec-next.git --fetch
$ go run ./cmd/lvh kernels --dir _data build ipsec-next
INFO[0000] Configuring kernel                           
Error: failed to configure kernel: unsupported architecture 
exit status 1

I needed to pass --arch amd64.