Add an offset to cranelift-wasm's GlobalVariable.

lib/wasm/src/lib.rs

@@ -36,6 +36,7 @@
 extern crate cranelift_codegen;
 #[macro_use]
 extern crate cranelift_entity;
+extern crate cast;
 extern crate cranelift_frontend;
 #[cfg(test)]
 extern crate target_lexicon;