RPATH and $ORIGIN

HPUX:
HP-UX Linker and Libraries User's Guide

Linker Tools for Itanium-Based Systems, chatr

Determining How to Link Programs or Libraries (Linker Tasks)

For HPUX/PA-RISC 32-bits, it uses SOM file format. (very similiar to aout format)
Others, ELF is used.

Linux:
ld.so, ld-linux.so* — dynamic linker/loader

UsingOrigin - SCons Wiki

ELF is used.

Solaris:
C. Recording Dependencies with $ORIGIN (Linker and Libraries Guide) - Sun Microsystems

ELF is used.

AIX:
There is no such thing. AIX uses XCOFF for their executable/shared library file format.
It is possible to write a program to modify these setting.