From comp.sys.mac.programmer.help
To instruct ld to link against a library called ‘libName’ you specify
the linker flag ‘-lName’. That’s the rule. To link against libxml2.dylyb
you would pass ‘-lxml2′. If you look in /usr/lib (on 10.5) you’ll see
that this is acutally a symlink to the currently shipped version
libxml2.2.dylib.