`fontconfig` through the FFI: best practice?

[Matthew Butterick]

If I want to call functions in the `fontconfig` library through the FFI, 

should I be relying on the incantations in "cairo-lib.rkt"?  [1] 

Or are those somehow specific to the `racket/draw` system? 

Why does the `fontconfig-lib` definition there include libraries that are not `libfontconfig`? 

Does the "Racket-specific patch to Fontconfig" need to be used always?

So far I've gotten some Fontconfig code to work on Racket 7.1 @ Mojave but it failed on 7.1 @ Sierra. So there is some platform-specific magic I'm missing. 

[1] https://github.com/racket/draw/blob/6ada7d8abdc664b4b4b42c6e2a7a3703d3794f9e/draw-lib/racket/draw/unsafe/cairo-lib.rkt