cond-expand is dumb and its name is dumber. Take libgsl.scm; different versions of the GSL library have different functions. We need to know when we're building the FFI what GSL version we're dealing with. It would be nuts to start pushing and checking dozens of library version symbols when all we actually want is (> version 23.19). In place of cond-expand, s7 uses reader-cond, so the read-time decision involves normal Scheme evaluation.
meh