At the top-level, you create a GNUmakefile that will drive the building of the subdirectories. Here is an example:
include $(GNUSTEP_MAKEFILES)/common.make SERIAL_SUBDIRECTORIES = Source Tools include $(GNUSTEP_MAKEFILES)/serial-subdirectories.make
This will cause gnustep-make to go into the SERIAL_SUBDIRECTORIES in order, and build them serially, one by one. So, it will first build Source (that contains our library) and then Tools (that contains our tool).
If you want the two subdirectories to be built in parallel, you just need to use parallel-subdirectories.make, as follows:
include $(GNUSTEP_MAKEFILES)/common.make PARALLEL_SUBDIRECTORIES = Source Tools include $(GNUSTEP_MAKEFILES)/parallel-subdirectories.make
This will tell gnustep-make that it should fork off two subprocesses, and build the Source and Tools subdirectories in parallel.