This is the last `@mut` in `librustc` that does not depend on libsyntax.

(implicitly) less_eq.

Closes #11035

If it's a trait method, this checks the stability attribute of the
method inside the trait definition. Otherwise, it checks the method
implementation itself.

Also remove all instances of 'self within the codebase.

This fixes #10889.

This replaces the link meta attributes with a pkgid attribute and uses a hash
of this as the crate hash. This makes the crate hash computable by things
other than the Rust compiler. It also switches the hash function ot SHA1 since
that is much more likely to be available in shell, Python, etc than SipHash.

Fixes #10188, #8523.

This bug showed up because the visitor only visited the path of the implemented
trait via walk_path (with no corresponding visit_path function). I have modified
the visitor to use visit_path (which is now overridable), and the privacy
visitor overrides this function and now properly checks for the privacy of all
paths.

Closes #10857

Closes #10853

Because the root module isn't actually an item, we need to do some hackish
handling of it.

Closes #10656.

Instead of forcibly always aborting compilation, allow usage of
 #[warn(unknown_features)] and related lint attributes to selectively abort
 compilation. By default, this lint is deny.

This provides a building block for fast thread-local storage. It does
not change the safety semantics of `static mut`.

Closes #10310

and librustpkg.

This also moves `#[auto_{en,de}code]` checker from syntax to lint.

Bringing it into line with the unused-variable one,

    fn main() {
        let mut _a = 1;
    }

will not warn that `_a` is never used mutably.

Fixes #6911.

Previously, the `exported_items` set created by the privacy pass was
incomplete. Specifically, it did not include items that had been defined
at a private path but then `pub use`d at a public path. This commit
finds all crate exports during the privacy pass. Consequently, some code
in the reachable pass and in rustdoc is no longer necessary. This commit
then removes the separate `MissingDocLintVisitor` lint pass, opting to
check missing_doc lint in the same pass as the other lint checkers using
the visibility result computed by the privacy pass.

Fixes #9777.