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.