Port core util lib to support no_std

src/stack_height/mod.rs

@@ -48,6 +48,9 @@
 //!   between the frames.
 //! - upon entry into the function entire stack frame is allocated.
 
+use std::string::String;
+use std::vec::Vec;
+
 use parity_wasm::elements::{self, Type};
 use parity_wasm::builder;