Reformat use declarations.

The previous commit updated `rustfmt.toml` appropriately. This commit is
the outcome of running `x fmt --all` with the new formatting options.

compiler/rustc_arena/src/lib.rs

@@ -27,15 +27,14 @@
 #![feature(strict_provenance)]
 // tidy-alphabetical-end
 
-use smallvec::SmallVec;
-
 use std::alloc::Layout;
 use std::cell::{Cell, RefCell};
 use std::marker::PhantomData;
 use std::mem::{self, MaybeUninit};
 use std::ptr::{self, NonNull};
-use std::slice;
-use std::{cmp, intrinsics};
+use std::{cmp, intrinsics, slice};
+
+use smallvec::SmallVec;
 
 /// This calls the passed function while ensuring it won't be inlined into the caller.
 #[inline(never)]

compiler/rustc_arena/src/tests.rs

@@ -1,8 +1,10 @@
 extern crate test;
-use super::TypedArena;
 use std::cell::Cell;
+
 use test::Bencher;
 
+use super::TypedArena;
+
 #[allow(dead_code)]
 #[derive(Debug, Eq, PartialEq)]
 struct Point {