Due to a bug in rust-bindgen, use the bindings as generated on the Mac
for the same version of MagickWand as found on FreeBSD. That is, when
build.rs is invoked on a FreeBSD system, it will use the Mac-generated
bindings.rs rather than pulling down rust-bindgen and invoking it to
generate the bindings on the fly. See issue #385 in the rust-bindgen
project for details.
cargo test passes
