Incl. functional changes, especially wrt. preserved paths for object files
(previously only when creating a static/dynamic library, now only if
specifying the -op switch).
Notably, the glue layer side of the changed multiple interface
inheritance layout (DMD a54e89d) has not been implemented yet.
This corresponds to DMD commit 3f6a763c0589dd03c1c206eafd434b593702564e.