Fix a fallout from SSP commit, and make this compile again.

Bonus: including kern.mk just to pick kernel warning flags
was an extremely bad idea anyway, because it also picked
up CFLAGS (it probably wasn't the case at the time of CVS
rev. 1.1, I haven't checked).  Remove duplicate CWARNFLAGS
from CFLAGS.

sys/boot/pc98/boot2/Makefile

@@ -12,7 +12,6 @@ CFLAGS=		-Os -mrtd \
 		-fno-unit-at-a-time \
 		-D_KERNEL -DBOOTWAIT=${BOOTWAIT} -DTIMEOUT=${TIMEOUT}
 CFLAGS+=	-DBOOTSEG=${BOOTSEG} -DBOOTSTACK=${BOOTSTACK}
-CFLAGS+=	${CWARNFLAGS}
 CFLAGS+=	-I${.CURDIR}/../../.. -I.
 
 # By default, if a serial port is going to be used as console, use COM1
@@ -110,5 +109,5 @@ i386:
 
 CLEANFILES+=	machine i386
 
-.include "${.CURDIR}/../../../conf/kern.mk"
+CWARNFLAGS!=	${MAKE} -f bsd.own.mk -f ${.CURDIR}/../../../conf/kern.mk -V CWARNFLAGS
 .include <bsd.prog.mk>