Auto merge of rust-lang#3357 - RalfJung:imports, r=RalfJung

reorder rustc crate imports a bit

Author: bors

src/tools/miri/src/bin/miri.rs

@@ -8,6 +8,11 @@
     rustc::untranslatable_diagnostic
 )]
 
+// Some "regular" crates we want to share with rustc
+#[macro_use]
+extern crate tracing;
+
+// The rustc crates we need
 extern crate rustc_data_structures;
 extern crate rustc_driver;
 extern crate rustc_hir;
@@ -16,8 +21,6 @@ extern crate rustc_log;
 extern crate rustc_metadata;
 extern crate rustc_middle;
 extern crate rustc_session;
-#[macro_use]
-extern crate tracing;
 
 use std::env::{self, VarError};
 use std::num::NonZero;

src/tools/miri/src/lib.rs

@@ -49,8 +49,12 @@
 // Needed for rustdoc from bootstrap (with `-Znormalize-docs`).
 #![recursion_limit = "256"]
 
-extern crate either; // the one from rustc
+// Some "regular" crates we want to share with rustc
+extern crate either;
+#[macro_use]
+extern crate tracing;
 
+// The rustc crates we need
 extern crate rustc_apfloat;
 extern crate rustc_ast;
 extern crate rustc_const_eval;
@@ -63,11 +67,8 @@ extern crate rustc_middle;
 extern crate rustc_session;
 extern crate rustc_span;
 extern crate rustc_target;
-#[macro_use]
-extern crate tracing;
-
-// Necessary to pull in object code as the rest of the rustc crates are shipped only as rmeta
-// files.
+// Linking `rustc_driver` pulls in the required  object code as the rest of the rustc crates are
+// shipped only as rmeta files.
 #[allow(unused_extern_crates)]
 extern crate rustc_driver;