appliance: Refactor the TAR_COMMAND macro

No change, just make it easier to understand.

Updates: commit 53632b4b82

appliance/Makefile.am

@@ -113,8 +113,9 @@ packagelist: packagelist.in Makefile guestfsd.deps
 	cmp -s $@ $@-t || mv $@-t $@
 	rm -f $@-t
 
-# Use stable times and owner/group (RHBZ#2320025).
-TAR_COMMAND := tar -z \
+# Use stable owner/group and mtimes (RHBZ#2320025).
+TAR_OPTIONS := \
+	-z \
 	--owner=0 --group=0 \
 	$${SOURCE_DATE_EPOCH:+--mtime=@"$$SOURCE_DATE_EPOCH"}
 
@@ -123,7 +124,7 @@ supermin.d/daemon.tar.gz: ../daemon/guestfsd
 	rm -rf tmp-d
 	mkdir -p tmp-d$(DAEMON_SUPERMIN_DIR) tmp-d/etc
 	ln ../daemon/guestfsd tmp-d$(DAEMON_SUPERMIN_DIR)/guestfsd
-	( cd tmp-d && $(TAR_COMMAND) -cf - * ) > $@-t
+	( cd tmp-d && tar $(TAR_OPTIONS) -cf - * ) > $@-t
 	rm -r tmp-d
 	mv $@-t $@
 
@@ -144,7 +145,7 @@ supermin.d/hostfiles: hostfiles.in Makefile
 
 supermin.d/init.tar.gz: init
 	rm -f $@ $@-t
-	( cd $(srcdir) && $(TAR_COMMAND) -cf - init ) > $@-t
+	( cd $(srcdir) && tar $(TAR_OPTIONS) -cf - init ) > $@-t
 	mv $@-t $@
 
 # We should put this file in /lib/udev/rules.d, but put it in /etc so
@@ -154,7 +155,7 @@ supermin.d/udev-rules.tar.gz: 99-guestfs-serial.rules
 	rm -rf tmp-u
 	mkdir -p tmp-u/etc/udev/rules.d
 	for f in $^; do ln $$f tmp-u/etc/udev/rules.d/$$(basename $$f); done
-	( cd tmp-u && $(TAR_COMMAND) -cf - etc ) > $@-t
+	( cd tmp-u && tar $(TAR_OPTIONS) -cf - etc ) > $@-t
 	rm -r tmp-u
 	mv $@-t $@