This would allow interested parties to do experimental runs with an
environment set appropriately to raise all the warnings throughout the
build; e.g. env WARNS=6 NO_WERROR=yes buildworld.
Not currently touching the numerous instances in ^/tools.
MFC after: 1 week
Simplifying maintainance and options (only one place to deal with MK_DMAGENT)
This also makes packaging base less intrusive by getting a single point where
to add tags.
