sys/conf/files aicasm

I can't say I understand much about the syntax of the top part of
sys/conf/files, but this line:


aicasm				optional ahc | ahd			   \
	dependency	"$S/dev/aic7xxx/aicasm/*.[chyl]"		   \
	compile-with	"CC='${CC}' ${MAKE} -f $S/dev/aic7xxx/aicasm/Makefile
MAKESRCPATH=$S/dev/aic7xxx/aicasm" \
	no-obj no-implicit-rule						   \
	clean		"aicasm* y.tab.h"

looks to me like aicasm should only be built if I have device ahc or
device ahd in my kernel configuration file.

But even if I make a config file without those devices (e.g. by doing
include GENERIC then nodevices ahc, ahd) the file is still built.  Am
I missing something about how these lines in sys/conf/files work?

As a side question, why does the Makefile for dev/aic7xxx/aicasm have
-I/usr/include in CFLAGS instead of using some marcos to get to the
source tree I'm actually building from?

Thanks,
matthew