Small update, I pushed a change to i3ipcpp that also builds a shared library in addition to the static library. (The i3ipcpp patches I will probably be able to send upstream at some point). polybar correctly uses the shared library, I think it's better this way.
I don't think I can do the same with xpp, since it is a header only library and a shared library would probably be pointless. I think I can even remove the static library (libxpp.a); it's empty. The static linkage happens with the xcb libraries anyway, not with xpp. -- Jason Pleau