add required imports & feature

src/librustc_data_structures/array_vec.rs

@@ -19,6 +19,7 @@ use std::slice;
 use std::fmt;
 use std::mem;
 use std::collections::range::RangeArgument;
+use std::collections::Bound::{Excluded, Included, Unbounded};
 
 pub unsafe trait Array {
     type Element;

src/librustc_data_structures/lib.rs

@@ -27,6 +27,7 @@
 
 #![feature(shared)]
 #![feature(collections_range)]
+#![feature(collections_bound)]
 #![feature(nonzero)]
 #![feature(rustc_private)]
 #![feature(staged_api)]