xenstore-tools on NetBSD 10?

[Greg Troxel <gdt%lexort.com@localhost>]

It's marked ONLY_FOR NetBSD 5-9, and that seems obvious a mistake, but
before I fix it I wanted to ask.

My take is that pkgsrc formally supports only NetBSD 8 and up, but that
4 and older is so old that it doesn't make sense to accomodate them at
all, and thus this might as well just allow NetBSD.

If anyone is running NetBSD 4 or earlier and would be inconvenienced by
whatever happens if this is allowed to build (vs failing from ONLY_FOR),
please speak up.