The ADS IGES application is developed in a self-contained directory, intended to be added to the AutoCAD standard build environment as a directory named iges, at a peer level to ads, lisp, and the others. There's a Unix Makefile in the directory which obtains its ADS libraries from the ads directory in the build tree. This code was built on the Sun, but there's no Earthly reason it shouldn't run on any machine that supports ADS, once the appropriate build procedures are defined.
At the moment, for convenience in developing and debugging, a composite application called iges is built that implements both IGESIN and IGESOUT. It probably makes more sense for the final customer version to supply separate igesin and igesout applications, as one should rarely need both loaded at the same time. The code in autosim.c and the Makefile supports this partitioning into separate applications, although at the moment doing so requires manually changing some #defines at the top of autosim.c.