Enable and fix several more clippy lints.

lib/native/src/lib.rs

@@ -2,6 +2,20 @@
 //! Cretonne to generate code to run on the same machine.
 
 #![deny(missing_docs, trivial_numeric_casts, unused_extern_crates)]
+#![warn(unused_import_braces, unstable_features)]
+#![cfg_attr(feature = "clippy", plugin(clippy(conf_file = "../../clippy.toml")))]
+#![cfg_attr(feature = "cargo-clippy",
+            allow(new_without_default, new_without_default_derive))]
+#![cfg_attr(feature="cargo-clippy", warn(
+                float_arithmetic,
+                mut_mut,
+                nonminimal_bool,
+                option_map_unwrap_or,
+                option_map_unwrap_or_else,
+                print_stdout,
+                unicode_not_nfc,
+                use_self,
+                ))]
 
 extern crate cretonne_codegen;