From: David Ward on
gitlab.com
https://gitlab.com/cki-project/kernel-ark/-/merge_requests/1088#note_5662...
Exactly. Simply changing `%{variant}` to `.vanilla` would mean the
package name would become `kernel.vanilla` which is also invalid. While
it's possible to rework the way `%{vanilla}` is used in certain parts of
the SPEC file, I'm not really sure what the value is.
I assume the largest user of `--with-vanilla` is @knurd42 who maintains
https://fedoraproject.org/wiki/Kernel_Vanilla_Repositories.