undefined reference in mtsk_tty.c

[DeltaF1]

I'm currently trying to build this kernel as part of a PostmarketOS port and I get the following compilation error. I'm using GCC6/musl on alpine linux

armv7-alpine-linux-musleabihf-ld: drivers/built-in.o: in function `mtsk_tty_ioctl':
/home/pmos/build/src/lge-kernel-lproj-45d6b0c683f3e0178e91c081133c6ebbea1d30fd/drivers/char/diag/mtsk_tty.c:236: undefined reference to `mtsk_factory_mode'