SUBDIRS = $(wildcard */)

clean_SUBDIRS = $(addprefix clean_SUBDIRS_, $(SUBDIRS))

.PHONY: all clean clean_all $(clean_SUBDIRS)

all:

clean: clean_all

clean_all: $(clean_SUBDIRS)

$(clean_SUBDIRS):
	- $(MAKE) clean -C $(patsubst clean_SUBDIRS_%, %, $@)