kbuild: Do not write to builddir in modules_install

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: Christian Kujau <lists@nerdbynature.de>
Signed-off-by: Michal Marek <mmarek@suse.cz>

scripts/depmod.sh

@@ -21,13 +21,15 @@ fi
 # older versions of depmod require the version string to start with three
 # numbers, so we cheat with a symlink here
 depmod_hack_needed=true
-mkdir -p .tmp_depmod/lib/modules/$KERNELRELEASE
-if "$DEPMOD" -b .tmp_depmod $KERNELRELEASE 2>/dev/null; then
-	if test -e .tmp_depmod/lib/modules/$KERNELRELEASE/modules.dep -o \
-		-e .tmp_depmod/lib/modules/$KERNELRELEASE/modules.dep.bin; then
+tmp_dir=$(mktemp -d ${TMPDIR:-/tmp}/depmod.XXXXXX)
+mkdir -p "$tmp_dir/lib/modules/$KERNELRELEASE"
+if "$DEPMOD" -b "$tmp_dir" $KERNELRELEASE 2>/dev/null; then
+	if test -e "$tmp_dir/lib/modules/$KERNELRELEASE/modules.dep" -o \
+		-e "$tmp_dir/lib/modules/$KERNELRELEASE/modules.dep.bin"; then
 		depmod_hack_needed=false
 	fi
 fi
+rm -rf "$tmp_dir"
 if $depmod_hack_needed; then
 	symlink="$INSTALL_MOD_PATH/lib/modules/99.98.$KERNELRELEASE"
 	ln -s "$KERNELRELEASE" "$symlink"