build: don't require GLUON_TARGET for dirclean

Makefile

@@ -72,7 +72,7 @@ all: prepare-target
 prepare: prepare-target
 	+@$(GLUONMAKE) $@
 
-clean dirclean download images: FORCE
+clean download images: FORCE
 	@$(CheckExternal)
 	@$(CheckTarget)
 	+@$(GLUONMAKE_EARLY) maybe-prepare-target
@@ -102,6 +102,12 @@ manifest: FORCE
 		( [ ! -e $(BOARD_BUILDDIR)/prepared ] || ( $(GLUONMAKE) manifest GLUON_TARGET='$(GLUON_TARGET)' ) ) && \
 	) :)
 
+dirclean : FORCE
+	@for dir in build_dir dl staging_dir tmp; do \
+		rm -rf $(GLUON_ORIGOPENWRTDIR)/$$dir; \
+	done
+	@rm -rf $(GLUON_BUILDDIR) $(GLUON_IMAGEDIR)
+
 else
 
 TOPDIR=${CURDIR}
@@ -236,12 +242,6 @@ clean: FORCE
 	+$(SUBMAKE) clean
 	rm -f $(gluon_prepared_stamp)
 
-dirclean: FORCE
-	for dir in build_dir dl staging_dir tmp; do \
-		rm -rf $(GLUON_ORIGOPENWRTDIR)/$$dir; \
-	done
-	rm -rf $(GLUON_BUILDDIR)
-
 
 export MD5SUM := $(GLUONDIR)/scripts/md5sum.sh
 export SHA512SUM := $(GLUONDIR)/scripts/sha512sum.sh