Some packages are not yet ready for this. There are two demands: the install function of a library must be called install_<libname> and the Prolog side must use use_foreign_library/1 as
:- use_foreign_library(foreign(libname)).
Some packages (still) name the install function simply install(), but this obviously cannot work as you get a name conflict.
There may be other problems 
Only working on the Emscripten version with this option. PRs welcome 