debian: make sure KVER and KDIR are visible to dpkg build

The debuild clears up the environment, thus the essential SCST variables
KVER and KDIR are cleared out. This patch fixes it.

Note: technically, `debild` supports `--preserve-env` option. But in
reality making use of it makes no difference, variables still do not
appear. Work around it by using DEB_foo_SET from `man dpkg-buildflags`

Makefile

@@ -387,7 +387,7 @@ dpkg: ../scst_$(VERSION).orig.tar.gz
 	else								\
 	  buildopts+=(-j4);						\
 	fi &&								\
-	debuild "$${buildopts[@]}" --lintian-opts --profile debian &&   \
+	DEB_KVER_SET=$(KVER) DEB_KDIR_SET=$(KDIR) debuild "$${buildopts[@]}" --lintian-opts --profile debian && \
 	mkdir -p dpkg &&						\
 	for f in "$${output_files[@]}" ../scst_$(VERSION).orig.tar.[gx]z; do\
 		mv $$f dpkg || true;					\

debian/rules

@@ -17,6 +17,11 @@ SUBDIRS=scst fcst iscsi-scst qla2x00t/qla2x00-target scst_local scstadmin srpt
 DESTDIR=$(CURDIR)/debian/tmp
 VERSION:=$(shell head -n1 debian/changelog | sed 's/.*(\([0-9.]*\).*).*/\1/')
 
+# rules won't see variables unless they're using DEB_foo_SET syntax. So use that as
+# an intermediary. Also, export variables for sub-makes to be able to see them.
+export KVER=$(DEB_KVER_SET)
+export KDIR=$(DEB_KDIR_SET)
+
 %:
 	echo "*** dh $@ ***"
 	dh $@