It is desirable to declare standard libraries available on a given system. Putting target declaration in Jamfile is not really good, since locations of the libraries can vary. The solution is to put the following to site-config.jam.

import project ;
project.initialize $(__name__) ;
project site-config ;
lib zlib : : <name>z ;

The second line allows this module to act as project. The third line gives id to this project — it really has no location and cannot be used otherwise. The fourth line just declares a target. Now, one can write:

exe hello : hello.cpp /site-config//zlib ;

in any Jamfile.