Use tidy to sort crate attributes for all compiler crates.

We already do this for a number of crates, e.g. `rustc_middle`,
`rustc_span`, `rustc_metadata`, `rustc_span`, `rustc_errors`.

For the ones we don't, in many cases the attributes are a mess.
- There is no consistency about order of attribute kinds (e.g.
  `allow`/`deny`/`feature`).
- Within attribute kind groups (e.g. the `feature` attributes),
  sometimes the order is alphabetical, and sometimes there is no
  particular order.
- Sometimes the attributes of a particular kind aren't even grouped
  all together, e.g. there might be a `feature`, then an `allow`, then
  another `feature`.

This commit extends the existing sorting to all compiler crates,
increasing consistency. If any new attribute line is added there is now
only one place it can go -- no need for arbitrary decisions.

Exceptions:
- `rustc_log`, `rustc_next_trait_solver` and `rustc_type_ir_macros`,
  because they have no crate attributes.
- `rustc_codegen_gcc`, because it's quasi-external to rustc (e.g. it's
  ignored in `rustfmt.toml`).

compiler/rustc_serialize/src/lib.rs

@@ -1,20 +1,22 @@
 //! Support code for encoding and decoding types.
 
+// tidy-alphabetical-start
+#![allow(internal_features)]
+#![allow(rustc::internal)]
+#![cfg_attr(test, feature(test))]
 #![doc(
     html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/",
     html_playground_url = "https://play.rust-lang.org/",
     test(attr(allow(unused_variables), deny(warnings)))
 )]
 #![doc(rust_logo)]
-#![allow(internal_features)]
-#![feature(rustdoc_internals)]
 #![feature(const_option)]
 #![feature(core_intrinsics)]
 #![feature(min_specialization)]
 #![feature(never_type)]
 #![feature(ptr_sub_ptr)]
-#![cfg_attr(test, feature(test))]
-#![allow(rustc::internal)]
+#![feature(rustdoc_internals)]
+// tidy-alphabetical-end
 
 pub use self::serialize::{Decodable, Decoder, Encodable, Encoder};