Fix the subdirs logic so it works with GNU make 3.80

Fix the subdirs logic so it works with GNU make 3.80

The previous fix which fixed the problem with GNU make 3.81 building
all of the library object files caused GNU make 3.80 fail because the
subdirectories (such as elfshared) were not getting created.  This fix
should allow the Makefiles to work with both GNU make 3.80 and GNU
make 3.81.