One of the recent commits by sephe caused genassym.c to depend on
bus_if.h and device_if.h (via machintr.h via bus.h).
However, without -j, these headers would not be generated (from
the .m files) before genassym.c was compiled, causing the kernel
build to break.
As a fix, make genassym.c depend on these headers in the Makefile.
The interesting bit is that this is one of the cases where it
breaks without -j but _does_ work with -j 1 (read: one) due to
the different handling of no -j vs. -j 1 in make(1).
assym.s: $S/kern/genassym.sh genassym.o
sh $S/kern/genassym.sh genassym.o > ${.TARGET}
-genassym.o: $S/platform/$P/$M/genassym.c ${FORWARD_HEADERS_COOKIE}
+genassym.o: $S/platform/$P/$M/genassym.c ${FORWARD_HEADERS_COOKIE} \
+ ${MFILES:T:S/.m$/.h/}
${CC} -c ${CFLAGS:N-fno-common:N-mcmodel=small} ${WERROR} \
$S/platform/$P/$M/genassym.c