SUBDIRS=my_lib product
LIBDIR=lib

.PHONY: clean subdirs $(SUBDIRS)

subdirs: $(SUBDIRS)

$(SUBDIRS):
	$(MAKE) -C $@

all: $(LIBDIR) subdirs

product: my_lib

$(LIBDIR):
	mkdir $@

clean:
	for dir in $(SUBDIRS); do \
		$(MAKE) -C $$dir clean; \
	done