rustc: embed path resolutions into the HIR instead of keeping DefMap.

src/test/compile-fail/issue-3521.rs

@@ -16,7 +16,7 @@ fn main() {
         Bar = foo
         //~^ ERROR attempt to use a non-constant value in a constant
         //~^^ ERROR constant evaluation error
-        //~| non-constant path in constant expression
+        //~| unresolved path in constant expression
     }
 
     println!("{}", Stuff::Bar);