It's a "bit" of a PITA.
c.f.,
https://github.com/NiLuJe/FBInk/blob...i/fbink_decl.c (which isn't entirely up-to-date)
Then mangle the output from ffi-cdecl into py-fbink's build.py, then build that in a cross-aware fashion (I'm using a patched distutilscross, because upstream is dead; but crossenv should work).
I... wouldn't recommend attempting any of that unless you already have experience cross-compiling Python 3 modules, because it's an hilariously awful experience.