The dependency on libcrypt has absolutely nothing to do with AOLserver, the Postgres driver, or OpenACS.
The dependency was added late in POSTGRES (as opposed to any of the above components) late in the Beta cycle. It was well-documented in Postgres land, but folks who arrive at Postgres via our narrow little view of life may well have missed it.
In fact, it sorta snuck under our radar. You can fully expect that future versions of the Makefile involved will include "-lcrypt".
The error comes from the Postgres API library. We just link it in, and when the dependency was added, our links failed. That's the long and short. "-lcrypt" won't hurt if you don't need it...