Say "Global Variable" when referring to the WebAssembly concept.

This helps avoid confusion between wasm global variables and cretonne
global values.

lib/wasm/src/sections_translator.rs

@@ -4,7 +4,7 @@
 //! The code of theses helper function is straightforward since it is only about reading metadata
 //! about linear memories, tables, globals, etc. and storing them for later use.
 //!
-//! The special case of the initialize expressions for table elements offsets or global values
+//! The special case of the initialize expressions for table elements offsets or global variables
 //! is handled, according to the semantics of WebAssembly, to only specific expressions that are
 //! interpreted on the fly.
 use cretonne_codegen::ir::{self, AbiParam, Signature};