…crum

Stabilize rc_downcast

Fixes rust-lang#44608

Rollup of 9 pull requests

Successful merges:

 - #51901 (Rc: remove unused allocation and fix segfault in Weak::new())
 - #52058 (Use of unimplemented!() causing ICE with NLL)
 - #52067 (Visit the mir basic blocks in reverse-postfix order)
 - #52083 (Dont run ast borrowck on mir mode)
 - #52099 (fix typo in stable `--edition` error message)
 - #52103 (Stabilize rc_downcast)
 - #52104 (Remove unnecessary feature gate.)
 - #52117 (Dedupe filetime)
 - #52120 (ARM: expose the "mclass" target feature)

Failed merges:

r? @ghost

Version 1.29.0 (2018-09-13)
==========================

Compiler
--------
- [Bumped minimum LLVM version to 5.0.][51899]
- [Added `powerpc64le-unknown-linux-musl` target.][51619]
- [Added `aarch64-unknown-hermit` and `x86_64-unknown-hermit` targets.][52861]

Libraries
---------
- [`Once::call_once` now no longer requires `Once` to be `'static`.][52239]
- [`BuildHasherDefault` now implements `PartialEq` and `Eq`.][52402]
- [`Box<CStr>`, `Box<OsStr>`, and `Box<Path>` now implement `Clone`.][51912]
- [Implemented `PartialEq<&str>` for `OsString` and `PartialEq<OsString>`
  for `&str`.][51178]
- [`Cell<T>` now allows `T` to be unsized.][50494]
- [`SocketAddr` is now stable on Redox.][52656]

Stabilized APIs
---------------
- [`Arc::downcast`]
- [`Iterator::flatten`]
- [`Rc::downcast`]

Cargo
-----
- [Cargo can silently fix some bad lockfiles ][cargo/5831] You can use
  `--locked` to disable this behaviour.
- [`cargo-install` will now allow you to cross compile an install
  using `--target`][cargo/5614]
- [Added the `cargo-fix` subcommand to automatically move project code from
  2015 edition to 2018.][cargo/5723]

Misc
----
- [`rustdoc` now has the `--cap-lints` option which demotes all lints above
  the specified level to that level.][52354] For example `--cap-lints warn`
  will demote `deny` and `forbid` lints to `warn`.
- [`rustc` and `rustdoc` will now have the exit code of `1` if compilation
  fails, and `101` if there is a panic.][52197]
- [A preview of clippy has been made available through rustup.][51122]
  You can install the preview with `rustup component add clippy-preview`

Compatibility Notes
-------------------
- [`str::{slice_unchecked, slice_unchecked_mut}` are now deprecated.][51807]
  Use `str::get_unchecked(begin..end)` instead.
- [`std::env::home_dir` is now deprecated for its unintuitive behaviour.][51656]
  Consider using the `home_dir` function from
  https://crates.io/crates/dirs instead.
- [`rustc` will no longer silently ignore invalid data in target spec.][52330]

[52861]: rust-lang/rust#52861
[52656]: rust-lang/rust#52656
[52239]: rust-lang/rust#52239
[52330]: rust-lang/rust#52330
[52354]: rust-lang/rust#52354
[52402]: rust-lang/rust#52402
[52103]: rust-lang/rust#52103
[52197]: rust-lang/rust#52197
[51807]: rust-lang/rust#51807
[51899]: rust-lang/rust#51899
[51912]: rust-lang/rust#51912
[51511]: rust-lang/rust#51511
[51619]: rust-lang/rust#51619
[51656]: rust-lang/rust#51656
[51178]: rust-lang/rust#51178
[51122]: rust-lang/rust#51122
[50494]: rust-lang/rust#50494
[cargo/5614]: rust-lang/cargo#5614
[cargo/5723]: rust-lang/cargo#5723
[cargo/5831]: rust-lang/cargo#5831
[`Arc::downcast`]: https://doc.rust-lang.org/std/sync/struct.Arc.html#method.downcast
[`Iterator::flatten`]: https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.flatten
[`Rc::downcast`]: https://doc.rust-lang.org/std/rc/struct.Rc.html#method.downcast