More Makefile.unix tweaks

Drop some unneeded CINCLUDES.
Drop the VPATH stuff altogether.  It's entirely unused here, and some of
the paths in it don't even exist and apparently never have in this tree.
Drop the 'default' rule, without it there, 'all' already is the default.
Drop $(TARGET) from all, it already includes 'lib' which is $(TARGET).
Declare phony targets PHONY.