Upgrade to Rust 1.17.

- Remove some uses of 'static in const and static globals that are no
  longer needed.
- Use the new struct initialization shorthand.

lib/cretonne/src/ir/memflags.rs

@@ -7,7 +7,7 @@ enum FlagBit {
     Aligned,
 }
 
-const NAMES: [&'static str; 2] = ["notrap", "aligned"];
+const NAMES: [&str; 2] = ["notrap", "aligned"];
 
 /// Flags for memory operations like load/store.
 ///