r286727 breaks geom_md.ko loading

[Steve Kiernan]

On Wed, 16 Sep 2015 03:00:19 +0300
Gleb Smirnoff <glebius at FreeBSD.org> wrote:

>   Hi!
> 
>   There is regression after r286727. Our dynamic kernel linker doesn't
> support weak symbols, so the geom_md.ko can no longer be loaded dynamically
> neither from loader nor at runtime. Having it statically in kernel is
> the only working option.

The question in that case would be does it make sense to allow MD_ROOT when
building md as a kernel module?

-Steve