That library function looks supiciously like a solaris internal one, try "unsigned mod/divide" on for size and see how that fits as an interpretation.
What are you running Solaris on, a Sparc or x86?
Since psql works and depends on libpq, Postgres does seem to be properly installed. You might compare the link flags passed when linking it with the link flags passed when linking the postgres driver to make sure the system libraries are being referenced.
