You could, but you then have to recompile the world with this new information stored as a ELF header or something, and good luck if the library is not written in C (so it has its own conventions, ABI, memory model and binary format)
I'm talking about the status quo today, not how you can improve in a perfect world where everybody adopts a better way of doing things.
Implementing an half-baked Smalltalk layer on top of UNIX will not turn UNIX into a Smalltalk environment.
The calling convention can be assumed to be the same as used by the OS/arch combination.