I have noticed that the value of IB_LIB does not appear on your link line. At the moment I don't know why that happens (as you said with nwchem-6.1.1 this used to work). As a work around could you try modifying IB_LIB_NAME to
export IB_LIB_NAME="-L$(IB_LIB) $(IB_LIB_NAME)"
In the meantime I trying to figure out why the value of IB_LIB is no longer picked up.