and the error messages you got tell us that "struct userinfo" is not defined.
This suggests that neither os/aix.h nor any of the header files that it pulls in define the "userinfo" struct.
Yet, google suggests that the "userinfo" struct is to be found in /usr/include/procinfo.h, and os/aix.h definitely contains the line #include <procinfo.h>
First, check to see whether your /usr/include/procinfo.h does define the userinfo struct. If it does not, then the question that needs to be answered is "Why is it missing ?".
But if it does, then the question that needs to be answered is "How come I then get that error ?". (Is there another procinfo.h that gets loaded instead ?)
There's a few guys on p5p who are familiar with (and interested in) aix, so I think it's worth asking there if you strike out here.