Let depmod.sh create a temporary directory in /tmp instead of writing to
the build directory as root. The mktemp utility should be available on
any recent system (and there is already scripts/gen_initramfs_list.sh
relying on it).
Reported-by: NChristian Kujau <lists@nerdbynature.de>
Signed-off-by: NMichal Marek <mmarek@suse.cz>

depmod from module-init-tools < 3.13 and the busybox depmod check if the
kernel release starts with <num>.<num>.<num>. To support these versions,
we create a symlink with two numbers prepended.
Signed-off-by: NMichal Marek <mmarek@suse.cz>

Do not bloat the Makefile with multiline shell statements. No
user-visible change intended.
Signed-off-by: NMichal Marek <mmarek@suse.cz>