tidy up

src/librustc_mir/interpret/validity.rs

@@ -180,7 +180,7 @@ fn validate_scalar_type(
                     scalar_format(value), path, "a pointer");
                 let _fn = try_validation!(self.memory.get_fn(ptr),
                     scalar_format(value), path, "a function pointer");
-                // TODO: Check if the signature matches
+                // FIXME: Check if the signature matches
             }
             ty::FnDef(..) => {
                 // This is a zero-sized type with all relevant data sitting in the type.