Say "IR" instead of "IL".

While the specifics of these terms are debatable, "IR" generally
isn't incorrect in this context, and is the more widely recognized
term at this time.

See also the discussion in #267.

Fixes #267.

lib/wasm/src/environ/spec.rs

@@ -26,7 +26,7 @@ pub enum GlobalValue {
 /// Environment affecting the translation of a single WebAssembly function.
 ///
 /// A `FuncEnvironment` trait object is required to translate a WebAssembly function to Cretonne
-/// IL. The function environment provides information about the WebAssembly module as well as the
+/// IR. The function environment provides information about the WebAssembly module as well as the
 /// runtime environment.
 pub trait FuncEnvironment {
     /// Get the flags for the current compilation.