DESC
Include a check in the header to force the use of Large File Support.
EDESC
When linking an application that doesn't use Large File Support with the
library (which does), several problems might arise from the data size
differences.

It's very important that everything uses the same interface. Since there's no
portable way to force the application we're linking with uses LFS, we just
give an error in case they don't. It might seem uglier, but it's a lot safer.