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`).

Author: nnethercote

src/lib.rs

@@ -1,13 +1,16 @@
+// tidy-alphabetical-start
+#![allow(rustc::diagnostic_outside_of_impl)]
+#![allow(rustc::untranslatable_diagnostic)]
 #![cfg_attr(doc, allow(internal_features))]
-#![cfg_attr(doc, feature(rustdoc_internals))]
 #![cfg_attr(doc, doc(rust_logo))]
+#![cfg_attr(doc, feature(rustdoc_internals))]
+// Note: please avoid adding other feature gates where possible
 #![feature(rustc_private)]
 // Note: please avoid adding other feature gates where possible
-#![allow(rustc::diagnostic_outside_of_impl)]
-#![allow(rustc::untranslatable_diagnostic)]
 #![warn(rust_2018_idioms)]
-#![warn(unused_lifetimes)]
 #![warn(unreachable_pub)]
+#![warn(unused_lifetimes)]
+// tidy-alphabetical-end
 
 extern crate jobserver;
 #[macro_use]