Adapt relative RPATH and patht to sys.ji to LIBDIR

Since now LIBDIR can point to anywhere, and not only to a directory
immediately under PREFIX, it is not guaranteed that $(ORIGIN)/../$(JL_LIBDIR)
points to $(JL_LIBDIR).
Add BINDIR, LIBEXECDIR, DATADIR and INCLUDEDIR

These are needed to get the same directory layout under BUILD as after
installation under DESTDIR and eventually PREFIX.
Test