A proxy Makefile to subdirectory's Makefile

Makefile

# get all targets from subdirectory
SUBDIR := subdir
TARGETS := $(shell make -C $(SUBDIR) -rpn | sed -n -e "/^$$/ { n ; /^[^ .\#%][^ ]\*:/ { s/:.\*$$// ; p ; } ; }" )

# default target
all:

# pass all targets to subdirectory
%:
	make -C $(SUBDIR) $@

Suppose you have a subdirectory subdir under current, then any make command you do is just like you do it under subdir
For example:
make is the same as make -C subdir
make clean is the same as make -C subdir clean
Same for other targets