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

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

lib/wasm/src/lib.rs

@@ -43,7 +43,7 @@ mod state;
 mod translation_utils;
 
 pub use environ::{
-    DummyEnvironment, FuncEnvironment, GlobalValue, ModuleEnvironment, WasmError, WasmResult,
+    DummyEnvironment, FuncEnvironment, GlobalVariable, ModuleEnvironment, WasmError, WasmResult,
 };
 pub use func_translator::FuncTranslator;
 pub use module_translator::translate_module;