Don't build folders without Makefile

Makefile

@@ -148,21 +148,23 @@ $(ARNAME): $(SUBDIRS) $(LOCALOBJECTS)
 
 .PHONY: $(SUBDIRS)
 $(SUBDIRS):
-	@depth=$(MAKELEVEL); \
-	while [ $${depth} -gt 0 ] ; do \
-		echo -n " "; \
-		depth=`expr $$depth - 1`; \
-	done; \
-	true
-	@echo " <$@>"
-	@$(MAKE) -s -S -C $@ artifacts $(ARCH)
-	@depth=$(MAKELEVEL); \
-	while [ $${depth} -gt 0 ] ; do \
-		echo -n " "; \
-		depth=`expr $$depth - 1`; \
-	done; \
-	true
-	@echo " </$@>"
+	@if [ -e "$@/Makefile" ]; then \
+		depth=$(MAKELEVEL); \
+		while [ $${depth} -gt 0 ] ; do \
+			echo -n " "; \
+			depth=`expr $$depth - 1`; \
+		done; \
+		true; \
+		echo " <$@>"; \
+		$(MAKE) -s -S -C $@ artifacts $(ARCH); \
+		depth=$(MAKELEVEL); \
+		while [ $${depth} -gt 0 ] ; do \
+			echo -n " "; \
+			depth=`expr $$depth - 1`; \
+		done; \
+		true; \
+		echo " </$@>"; \
+	fi
 
 .PHONY: all
 all: $(TARGETS)