This patch adds the necessary pieces to support rust on Bitrig https://bitrig.org

Continued from #22520

p=1 please

The old suffixes now issue warnings unless a feature-gate is given.

Fixes #22496.

r? @alexcrichton 

p=1 please

Take 2. This PR includes a bunch of refactoring that was part of an experimental branch implementing [implied bounds]. That particular idea isn't ready to go yet, but the refactoring proved useful for fixing #22246. The implied bounds branch also exposed #22110 so a simple fix for that is included here. I still think some more refactoring would be a good idea here -- in particular I think most of the code in wf.rs is kind of duplicating the logic in implicator and should go, but I decided to post this PR and call it a day before diving into that. I'll write a bit more details about the solutions I adopted in the various bugs. I patched the two issues I was concerned about, which was the handling of supertraits and HRTB (the latter turned out to be fine, so I added a comment explaining why.)

r? @pnkfelix (for now, anyway)
cc @aturon 

[implied bounds]: http://smallcultfollowing.com/babysteps/blog/2014/07/06/implied-bounds/

Conflicts:
	src/librustc/middle/infer/combine.rs
	src/librustc_typeck/check/wf.rs

Conflicts:
	src/libcollections/slice.rs
	src/libcollections/str.rs
	src/librustc/middle/lang_items.rs
	src/librustc_back/rpath.rs
	src/librustc_typeck/check/regionck.rs
	src/libstd/ffi/os_str.rs
	src/libsyntax/diagnostic.rs
	src/libsyntax/parse/parser.rs
	src/libsyntax/util/interner.rs
	src/test/run-pass/regions-refcell.rs

Conflicts:
	src/libcollections/btree/map.rs
	src/libcollections/str.rs
	src/libcollections/vec.rs
	src/libcore/borrow.rs
	src/libcore/hash/mod.rs
	src/libstd/collections/hash/map.rs
	src/libstd/collections/hash/set.rs

This commit stabilizes `std::borrow`, making the following modifications
to catch up the API with language changes:

* It renames `BorrowFrom` to `Borrow`, as was originally intended (but
  blocked for technical reasons), and reorders the parameters
  accordingly.

* It moves the type parameter of `ToOwned` to an associated type. This
  is somewhat less flexible, in that each borrowed type must have a
  unique owned type, but leads to a significant simplification for
  `Cow`. Flexibility can be regained by using newtyped slices, which is
  advisable for other reasons anyway.

* It removes the owned type parameter from `Cow`, making the type much
  less verbose.

* Deprecates the `is_owned` and `is_borrowed` predicates in favor of
  direct matching.

The above API changes are relatively minor; the basic functionality
remains the same, and essentially the whole module is now marked
`#[stable]`.

[breaking-change]

support warnings.

Conflicts:
	src/librustc_trans/trans/tvec.rs

Conflicts:
	src/libcollections/bit.rs
	src/libcollections/linked_list.rs
	src/libcollections/vec_deque.rs
	src/libstd/sys/common/wtf8.rs

cc #22240

This commit is an implementation of [RFC 592][r592] and [RFC 840][r840]. These
two RFCs tweak the behavior of `CString` and add a new `CStr` unsized slice type
to the module.

[r592]: https://github.com/rust-lang/rfcs/blob/master/text/0592-c-str-deref.md
[r840]: https://github.com/rust-lang/rfcs/blob/master/text/0840-no-panic-in-c-string.md

The new `CStr` type is only constructable via two methods:

1. By `deref`'ing from a `CString`
2. Unsafely via `CStr::from_ptr`

The purpose of `CStr` is to be an unsized type which is a thin pointer to a
`libc::c_char` (currently it is a fat pointer slice due to implementation
limitations). Strings from C can be safely represented with a `CStr` and an
appropriate lifetime as well. Consumers of `&CString` should now consume `&CStr`
instead to allow producers to pass in C-originating strings instead of just
Rust-allocated strings.

A new constructor was added to `CString`, `new`, which takes `T: IntoBytes`
instead of separate `from_slice` and `from_vec` methods (both have been
deprecated in favor of `new`). The `new` method returns a `Result` instead of
panicking.  The error variant contains the relevant information about where the
error happened and bytes (if present). Conversions are provided to the
`io::Error` and `old_io::IoError` types via the `FromError` trait which
translate to `InvalidInput`.

This is a breaking change due to the modification of existing `#[unstable]` APIs
and new deprecation, and more detailed information can be found in the two RFCs.
Notable breakage includes:

* All construction of `CString` now needs to use `new` and handle the outgoing
  `Result`.
* Usage of `CString` as a byte slice now explicitly needs a `.as_bytes()` call.
* The `as_slice*` methods have been removed in favor of just having the
  `as_bytes*` methods.

Closes #22469
Closes #22470
[breaking-change]