This is wrong:

On Sat, Sep 27, 2003 at 12:11:55PM +0100, Chris Pinnock wrote:
> Setting OBJMACHINE to that will just change the name of the object
> directories to obj.i686 (if you use object directories to seperate
> binary objects from the source tree).

...so correcting myself here...

OBJMACHINE      If this is set but MAKEOBJDIR is not set, creates
                object directories or links named "obj.${MACHINE}";
                otherwise, just creates ones named "obj".


See /usr/share/mk/bsd.README for more details.