CFLAGS=-Itestfiles -O2
CC=gcc
AR=ar
LDFLAGS=-Ltestfiles -lfoo

testfiles/target: testfiles/input.o testfiles/libfoo.a
	$(CC) $(CFLAGS) -o $@ $< $(LDFLAGS)

testfiles/libfoo.a: testfiles/foo.o testfiles/bar.o
	$(AR) crsv $@ $^

testfiles/foo.o: testfiles/foo.c testfiles/foo.h
	$(CC) $(CFLAGS) -o $@ -c $< 

testfiles/bar.o: testfiles/bar.c testfiles/bar.h
	$(CC) $(CFLAGS) -o $@ -c $< 

testfiles/input.o: testfiles/input.c testfiles/input.h testfiles/foo.h
	$(CC) $(CFLAGS) -o $@ -c $<

clean:
	rm -f testfiles/*.o testfiles/*.a testfiles/target