netbsd-rumpkernel: restrict archs
netbsd-rumpkernel: restrict archs

I don't think this is tested on other archs at all, and e.g.
does not support ppc64 ELFv2 ABI and possibly other specifics
for various archs, so go with a safe set.

[ci skip]

necrophcodr/void-packages,necrophcodr/void-packages,necrophcodr/void-packages,necrophcodr/void-packages,necrophcodr/void-packages