c/core/Makefile problem making lib/libtahu.so individually, and parallel make problems

[ian-abbott]

In "c/core/Makefile", the rule for target $(DNAME) does not create the "lib" directory as is done for the $(SNAME) target. That is a problem when running make lib/libtahu.so to build the dynamic library individually, and is also a problem when running make -j to build in parallel. The $(TEST) target does not depend on the built library files which could be a problem when running make -j to build in parallel.