The if_changed directive is useless against phony targets.
Reported-by: NStephen Rothwell <sfr@canb.auug.org.au>
Fixes: 2441e78b ("kbuild: better abstract vmlinux sequential prerequisites")
Signed-off-by: NNicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: NMichal Marek <mmarek@suse.cz>