To build a 64-bit application using the c89 utility, you must use the LP64 compiler option (i.e., -Wc,lp64) and the LP64 binder option (i.e., -Wl,lp64). The binder option is not actually passed to the binder. It is used by c89 to set up the appropriate link data sets.
To build a 64-bit application using the xlc utility, you do not have to explicitly specify the lp64 option on the command line for either the compile or the bind step. xlc uses the _64 command name suffix to ensure 64-bit compiles and binds.