From: Herton R. Krzesinski on
gitlab.com
https://gitlab.com/cki-project/kernel-ark/-/merge_requests/1035#note_5770...
Shouldn't RPM_VMLINUX_H have a default value? Is it a problem if it
isn't defined (when %artifacts is undefined) and ends up being passed as
```VMLINUX_H=""``` (empty)?