Using RELENG_8 to compile for older RELENG_x

[grarpamp]

This would simply involve downloading some canonical tarball, say
bind, and compiling it... perhaps even statically. Ports and it's
issues related to this would certainly not be considered.

I'd thought about the jails, emulation, installing 4.11 on spare
boxes [a] and whatnot.

Seemed there might be a more elegant way to cross compile and do
everything on the RELENG_8 box natively. Maybe by pointing the
toolchain at a copy of /lib /include from RELENG_4 or whatever.
Then expand that method to back compile for RELENG_x.

I think I'll try unpacking 4.11's release tarballs into an empty
jail, doing whatever else the install does and launching that. I'm
guessing I should be able to compile/install world/kernel/release/apps
in there. Assuming the running RELENG_8 parent kernel services don't
cause issues. If it doesn't work I can always fall back to [a].

Yeah, you could consider it 'embedded' all right. Like deep in a
dusty corner, driving some critical legacy shims that they forgot
about in the migration plan, oops.

As a side note, it would be nice if freebsd-archive containted
packages-x-stable too, copied over as part of the rm process from
the regular ftp.freebsd.org when it happens. And all the distfiles ever
used too, I don't think they're currently rm'ed though.