OK, since `void *' arithmetic should be banned I've added -Wpointer-arith
to all the sys/arch/xxx/conf/Makefile.xxx.
Doing that was interesting reading.  It seems that the enabled warning
vary from port to port.  Maybe we should try and make them all the same?

Some ports may break after this addition, but fixing the problems is
trivial, just add a cast to `char *'.

         -- Lennart