Compile of boot blocks fails, please help.

[Federico Canton]

Hello, I am trying to set a computer running FreeBSD 4.8-STABLE so that it
can boot using a serial console.  To this effect I am trying to compile new
boot blocks, but I get this error:

casa# cd /usr/src/sys/i386/boot/biosboot && make 
cc -O2 -malign-functions=0 -malign-jumps=0 -malign-loops=0  -DBOOTWAIT=5000
-DTIMEOUT= -DBOOTSEG=0x1000 -DBOOTSTACK=0xFFF0 -Wall -Wredundant-decls
-Wnested-externs -Wstrict-prototypes  -Wmissing-prototypes -Wpointer-arith
-Winline -Wcast-qual  -fformat-extensions -ansi -DCOMCONSOLE=0x3F8
-DCONSPEED=115200 -mpreferred-stack-boundary=2 -aout -nostdinc
-I/usr/src/sys/i386/boot/biosboot/../../../../include
-I/usr/src/sys/i386/boot/biosboot/../../.. -I/usr/src/sys/i386/boot/biosboot
-Wall -Wredundant-decls -Wnested-externs -Wstrict-prototypes
-Wmissing-prototypes -Wpointer-arith -Winline -Wcast-qual
-fformat-extensions -ansi  -N -T 0 -nostdlib -static -o boot start.o table.o
boot2.o boot.o asm.o bios.o serial.o probe_keyboard.o io.o disk.o sys.o 
serial.o: Undefined symbol `COMBRD' referenced from text segment
serial.o: Undefined symbol `COMBRD' referenced from text segment
*** Error code 1

Stop in /usr/src/sys/i386/boot/biosboot.
casa#

Can any one please help?

federico