Convenience macro for generating the module to hold the raw/unsafe ISPC bindings.
In addition to building the library with ISPC we use rust-bindgen to generate
a rust module containing bindings to the functions exported from ISPC. These
can be imported by passing the name of your library to the
#[macro_use] extern crate ispc_rt; // Functions exported from foo will be callable under foo::* ispc_module!(foo);