Move machine and other link creation to defs.mk

Steal the code from kmod.mk and use it to automatically create
links. Modify it a little for the needs of the loader (no need to
guess the OBJS dependency, and we have 32-on-64 cases to contend
with). Remove 15 redundant implementations (which were mostly
different, but kinda the same).

A future commit should factor out this code and that of kmod.mk so we
have only one copy of it in the tree.

Sposnored by: Netflix