[mir-opt] Fix mis-optimization and other issues with the SimplifyArmIdentity pass

This does not yet attempt re-enabling the pass, but it does resolve a number of issues with the pass.

r? @oli-obk

I believe this closes #73223.

Improve comments from #72617, as suggested by RalfJung

r? @RalfJung

Standardize bibliographic citations in rustc API docs

See #73877.

Create E0768

r? @Dylan-DPC

Use &raw in A|Rc::as_ptr

This PR uses `&raw` for offsetting `*mut [A]RcInner<T> -> *mut T`.

Additionally, this updates the implementation of `Weak::as_ptr` to support unsized `T`, though it does not yet relax the bounds of `Weak::as_ptr`/`into_raw`/`from_raw` to accept unsized `T`.

Use exhaustive match in const_prop.rs

Addresses a comment left by @RalfJung on #73613

r? @RalfJung

Add `format_args_capture` feature

This is the initial implementation PR for [RFC 2795](https://github.com/rust-lang/rfcs/pull/2795).

Note that, as dicussed in the tracking issue (#67984), the feature gate has been called `format_args_capture`.

Next up I guess I need to add documentation for this feature. I've not written any docs before for rustc / std so I would appreciate suggestions on where I should add docs.

Fallback to xml.etree.ElementTree

The xml.etree.cElementTree has been deprecated since Python 3.3
and removed in Python 3.9 https://bugs.python.org/issue36543.

Update cargo, rls

## cargo
14 commits in c26576f9adddd254b3dd63aecba176434290a9f6..fede83ccf973457de319ba6fa0e36ead454d2e20
2020-06-23 16:21:21 +0000 to 2020-07-02 21:51:34 +0000
- Fix overflow error on 32-bit. (rust-lang/cargo#8446)
- Exclude the target directory from backups using CACHEDIR.TAG (rust-lang/cargo#8378)
- CONTRIBUTING.md: Link to Zulip rather than Discord (rust-lang/cargo#8436)
- Update built-in help for features (rust-lang/cargo#8433)
- Update core-foundation requirement from 0.7.0 to 0.9.0 (rust-lang/cargo#8432)
- Parse `# env-dep` directives in dep-info files (rust-lang/cargo#8421)
- Move string interning to util (rust-lang/cargo#8419)
- Expose built cdylib artifacts in the Compilation structure (rust-lang/cargo#8418)
- Remove unused serde_derive dependency from the crates.io crate (rust-lang/cargo#8416)
- Remove unused remove_dir_all dependency (rust-lang/cargo#8412)
- Improve git error messages a bit (rust-lang/cargo#8409)
- Improve the description of Config.home_path (rust-lang/cargo#8408)
- Improve support for non-`master` main branches (rust-lang/cargo#8364)
- Document that OUT_DIR in JSON messages is an absolute path (rust-lang/cargo#8403)

## rls
2020-06-19 15:36:00 +0200 to 2020-06-30 23:34:52 +0200
- Update cargo (rust-lang-nursery/rls#1686)

Avoid `unwrap_or_else` in `RawVec::allocate_in`.

This reduces the amount of LLVM IR generated by up to 1 or 2%.

r? @Amanieu

If temporaries are used beyond just the temporary chain, then we can't
optimize out the reads and writes.

Rollup of 8 pull requests

Successful merges:

 - #73454 (Move contributing.md to rustc-dev-guide and point at getting started)
 - #73724 (Use WASM's saturating casts if they are available)
 - #73726 (resolve: disallow labelled breaks/continues through closures/async blocks)
 - #73753 (Use 'tcx for references to AccessLevels wherever possible.)
 - #73781 (Update psm version)
 - #73952 (Add option for local docker testing.)
 - #73957 (disable BTree min_max test in Miri for now)
 - #73975 (Document rustc_ast::ast::Pat)

Failed merges:

r? @ghost

Document rustc_ast::ast::Pat

disable BTree min_max test in Miri for now

Until https://github.com/rust-lang/rust/issues/73915 is fixed, better skip this test in Miri so that we can test the others at least.

Add option for local docker testing.

This adds the option `--dev` to `src/ci/docker/run.sh` so that it will enter an interactive environment for local testing. I have often needed this for testing things, but I always needed to edit this script. I wanted the ability to interact in the environment, run different commands, inspect errors, etc.

Update psm version

This new version includes a fix for building on aarch64 windows.

cc #72881

Use 'tcx for references to AccessLevels wherever possible.

Most of the changes are just fallout from removing a lifetime parameter from structs, and mostly in clippy.

r? @Manishearth

resolve: disallow labelled breaks/continues through closures/async blocks

Fixes #73541.

This PR modifies name resolution to prohibit labelled breaks/continues through closures or async blocks, fixing an ICE. In addition, it improves the diagnostics surrounding labelled breaks/continues through closures or async blocks by informing the user if the label exists in an parent scope and telling them that won't work.

r? @petrochenkov (resolve)
cc @estebank (diagnostic changes) @tmandry (issue is from `wg-async-foundations`)

Use WASM's saturating casts if they are available

WebAssembly supports saturating floating point to integer casts behind a target feature. The feature is already available on many browsers. Beginning with 1.45 Rust will start defining the behavior of floating point to integer casts to be saturating as well. For this Rust constructs additional checks on top of the `fptoui` / `fptosi` instructions it emits. Here we introduce the possibility for the codegen backend to construct saturating casts itself and only fall back to constructing the checks ourselves if that is not possible.

Resolves part of #73591

Move contributing.md to rustc-dev-guide and point at getting started

See description on https://github.com/rust-lang/rustc-dev-guide/pull/753

Remove `TypeckTables::empty(None)` and make hir_owner non-optional.

Each commit before the last one removes uses of `TypeckTables::empty(None)`, replacing the empty tables with having `Option` around the `&'tcx TypeckTables<'tcx>` that HIR visitors kept track of.

The last commit removes the concept of "empty `TypeckTables`" altogether, guaranteeing that every `TypeckTables` corresponds to a HIR body owner.

r? @nikomatsakis