added it to the /usr/src/sys/i386/conf/MYKERNEL. It's the module for my sound chip.
device snd_es137x

started building (as described in 'kernelconfig-building.html' of FreeBSD handbook)
# cd /usr/src
# make buildkernel KERNCONF=MYKERNEL

The out:
...........
............
..........
--------------------------------------------------------------
>>> stage 3.1: making dependencies
--------------------------------------------------------------
cd /usr/obj/usr/src/sys/MYKERNEL;  MAKEOBJDIRPREFIX=/usr/obj  MACHINE_ARCH=i386  MACHINE=i386  CPUTYPE=  GROFF_BIN_PATH=/usr/obj/usr/src/tmp/legacy/usr/bin  GROFF_FONT_PATH=/usr/obj/usr/src/tmp/legacy/usr/share/groff_font  GROFF_TMAC_PATH=/usr/obj/usr/src/tmp/legacy/usr/share/tmac  _SHLIBDIRPREFIX=/usr/obj/usr/src/tmp  INSTALL="sh /usr/src/tools/install.sh"  PATH=/usr/obj/usr/src/tmp/legacy/usr/sbin:/usr/obj/usr/src/tmp/legacy/usr/bin:/usr/obj/usr/src/tmp/legacy/usr/games:/usr/obj/usr/src/tmp/usr/sbin:/usr/obj/usr/src/tmp/usr/bin:/usr/obj/usr/src/tmp/usr/games:/sbin:/bin:/usr/sbin:/usr/bin make KERNEL=kernel depend -DNO_MODULES_OBJ
cc -c -O -pipe -Wall -Wredundant-decls -Wnested-externs -Wstrict-prototypes -Wmissing-prototypes -Wpointer-arith -Winline -Wcast-qual -fformat-extensions -std=c99 -g -nostdinc -I- -I. -I/usr/src/sys -I/usr/src/sys/contrib/altq -I/usr/src/sys/contrib/ipfilter -I/usr/src/sys/contrib/pf -I/usr/src/sys/contrib/dev/ath -I/usr/src/sys/contrib/dev/ath/freebsd -I/usr/src/sys/contrib/ngatm -I/usr/src/sys/dev/twa -D_KERNEL -DHAVE_KERNEL_OPTION_HEADERS -include opt_global.h -finline-limit=8000 --param inline-unit-growth=100 --param large-function-growth=1000 -mno-align-long-strings -mpreferred-stack-boundary=2 -mno-mmx -mno-3dnow -mno-sse -mno-sse2 -ffreestanding /usr/src/sys/i386/i386/genassym.c
NM='nm' sh /usr/src/sys/kern/genassym.sh genassym.o > assym.s
awk -f /usr/src/sys/tools/vnode_if.awk /usr/src/sys/kern/vnode_if.src -h
awk -f /usr/src/sys/tools/vnode_if.awk /usr/src/sys/kern/vnode_if.src -p
awk -f /usr/src/sys/tools/vnode_if.awk /usr/src/sys/kern/vnode_if.src -q
awk -f /usr/src/sys/tools/miidevs2h.awk /usr/src/sys/dev/mii/miidevs
awk -f /usr/src/sys/tools/pccarddevs2h.awk /usr/src/sys/dev/pccard/pccarddevs
awk -f /usr/src/sys/tools/usbdevs2h.awk /usr/src/sys/dev/usb/usbdevs -h
awk -f /usr/src/sys/tools/usbdevs2h.awk /usr/src/sys/dev/usb/usbdevs -d
awk -f /usr/src/sys/tools/vnode_if.awk /usr/src/sys/kern/vnode_if.src -c
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/dev/ata/ata_if.m -c
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/dev/eisa/eisa_if.m -c
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/dev/mii/miibus_if.m -c
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/dev/pccard/card_if.m -c
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/dev/pccard/power_if.m -c
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/dev/pci/pci_if.m -c
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/dev/pci/pcib_if.m -c
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/dev/ppbus/ppbus_if.m -c
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/dev/usb/usb_if.m -c
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/isa/isa_if.m -c
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/kern/bus_if.m -c
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/kern/cpufreq_if.m -c
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/kern/device_if.m -c
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/kern/linker_if.m -c
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/pci/agp_if.m -c
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/dev/acpica/acpi_if.m -c
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/dev/ata/ata_if.m -h
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/dev/eisa/eisa_if.m -h
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/dev/mii/miibus_if.m -h
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/dev/pccard/card_if.m -h
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/dev/pccard/power_if.m -h
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/dev/pci/pci_if.m -h
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/dev/pci/pcib_if.m -h
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/dev/ppbus/ppbus_if.m -h
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/dev/usb/usb_if.m -h
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/isa/isa_if.m -h
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/kern/bus_if.m -h
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/kern/cpufreq_if.m -h
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/kern/device_if.m -h
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/kern/linker_if.m -h
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/pci/agp_if.m -h
awk -f /usr/src/sys/tools/makeobjops.awk /usr/src/sys/dev/acpica/acpi_if.m -h
rm -f .newdep
make -V CFILES -V SYSTEM_CFILES -V GEN_CFILES |  MKDEP_CPP="cc -E" CC="cc" xargs mkdep -a -f .newdep -O -pipe  -Wall -Wredundant-decls -Wnested-externs -Wstrict-prototypes  -Wmissing-prototypes -Wpointer-arith -Winline -Wcast-qual  -fformat-extensions -std=c99 -g -nostdinc -I-  -I. -I/usr/src/sys -I/usr/src/sys/contrib/altq -I/usr/src/sys/contrib/ipfilter -I/usr/src/sys/contrib/pf -I/usr/src/sys/contrib/dev/ath -I/usr/src/sys/contrib/dev/ath/freebsd -I/usr/src/sys/contrib/ngatm -I/usr/src/sys/dev/twa -D_KERNEL -DHAVE_KERNEL_OPTION_HEADERS -include opt_global.h -fno-common -finline-limit=8000 --param inline-unit-growth=100 --param large-function-growth=1000  -mno-align-long-strings -mpreferred-stack-boundary=2  -mno-mmx -mno-3dnow -mno-sse -mno-sse2 -ffreestanding
*** Error code 1

Stop in /usr/obj/usr/src/sys/MYKERNEL.
*** Error code 1

Stop in /usr/src.
*** Error code 1

Stop in /usr/src.