Fix osx mangling hack
Fix osx mangling hack

Rust automatically adds one _ in the symbol. If we don't remove it, we will
endup getting three _.

emilio/rust-bindgen,emilio/rust-bindgen,rust-lang/rust-bindgen,emilio/rust-bindgen,emilio/rust-bindgen,rust-lang/rust-bindgen,rust-lang/rust-bindgen,rust-lang/rust-bindgen,emilio/rust-bindgen