Prevent a stray error message in the case that either DISTDIR or

DESTDIR is empty, by preventing readlink from being called in that
case.

Another option would be to use readlink -s, but that has the
undesirable effect of staying silent in situations other than empty
DISTDIR/DESTDIR

Signed-off-by: Aron Griffis <aron@hp.com>

tools/examples/Makefile

@@ -38,8 +38,8 @@ XEN_HOTPLUG_SCRIPTS = xen-backend.agent
 UDEV_RULES_DIR = /etc/udev
 UDEV_RULES = xen-backend.rules
 
-DI = $(shell readlink -f $(DISTDIR))
-DE = $(shell readlink -f $(DESTDIR))
+DI = $(if $(DISTDIR),$(shell readlink -f $(DISTDIR)),)
+DE = $(if $(DESTDIR),$(shell readlink -f $(DESTDIR)),)
 ifeq ($(findstring $(DI),$(DE)),$(DI))
 HOTPLUGS=install-hotplug install-udev
 else