- `ParamEnv::empty()` -- does not reveal all, good for typeck
- `ParamEnv::reveal_all()` -- does, good for trans
- `param_env.with_reveal_all()` -- converts an existing parameter environment

Improvements:

- Use Clone not Copy for the "simple cases"
- Separate TypeFoldable and Lift for the "simple cases"
- Support generics type parameters
- Support named fields in enum variants
- etc

Update the rls-rustc package

Should hopefully fix compiling the rls!

Rollup of 13 pull requests

- Successful merges: #48201, #48705, #48725, #48824, #48877, #48880, #48887, #48928, #48934, #48480, #48631, #48898, #48954
- Failed merges:

Add missing links

Remove auto trait implementation section when empty

Fixes #48882.

Remember state of top-level collapse toggle widget

This change allows the big top-right expand/collapse toggle to remember its setting across navigation or page reloads. Prior to this change, there was this annoyance:

- browse to some docs
- Click the minus button to collapse them
- browse to other docs (or reload the page)
- Everything is expanded again

The solution is based on storing a simple boolean flag in localStorage. I think it's a good improvement, but it does introduce the following potentially surprising behavior:

- browse to some docs
- click the minus button to collapse them
- click to expand a particular item (not the main top-right big one)
- reload the page, everything is collapsed

Paired with @debugsteven on this.

Clarify interfaction between File::set_len and file cursor

Should hopefully fix compiling the rls!

Fix hygene issue when deriving Debug

The code for several of the core traits doesn't use hygenic macros.
This isn't a problem, except for the Debug trait, which is the only
one that uses a variable, named "builder".

Variables can't share names with unit structs, so attempting to
[derive(Debug)] on any type while a unit struct with the name
"builder" was in scope would result in an error.

This commit just changes the name of the variable to
"__debug_trait_builder", because I couldn't figure out how to get a
list of all unit structs in-scope from within the derive expansion
function. If someone wants to have a unit struct with
the exact name "__debug_trait_builder", they'll just have to do it
without a [derive(Debug)].

I also checked the implementations of the other built-in derives to
ensure they didn't declare any variables.

in which some labels and notes are upgraded to structured suggestions

(Meanwhile, a couple of parse-fail tests are moved to UI tests so that
the reader can see the new output, and an existing UI test is given a
more evocative name.)

r? @estebank

Update stdsimd module

Pulls in a redesigned `std::simd` module as well as a replacement for the
`is_target_feature_detected!` macro

tidy: Add a check for stray `.stderr` and `.stdout` files in UI test directories

Add missing urls

r? @QuietMisdreavus

Propagating upstream code of conduct changes

[This repository's code of conduct](https://github.com/rust-lang/rust/blob/master/CODE_OF_CONDUCT.md) is out of sync with the [rust-www code of conduct](https://github.com/rust-lang/rust-www/blob/master/en-US/conduct.md) due changes from rust-lang/rust-www#1062. This PR propagates those changes and brings the files back into sync.

r? @steveklabnik

Update L4Re target specification

Due to the dynamically generated linker arguments of the L4Re build system, it is not a good idea to hard-code them in Rust. This PR undoes this step. It also adds an empty implementation to retrieve the number of CPUs.

Update Feature Request instructions

As noted in #48393 the contribution instructions for submitting a Feature Request are a little hasty, suggesting that the user immediately create an issue in the RFC repository. For users that want to submit a feature request, let's instead point them directly to the README file for the RFC repository, which contains detailed instructions on how to submit a Feature Request.

rephrase UnsafeCell doc

As shown by discussions on users.rust-lang.org [[1]], [[2]], UnsafeCell doc is not totally clear. I tried to made the doc univocal regarding what is allowed and what is not. The edits are based on my understanding following [[1]].

[1]: https://users.rust-lang.org/t/unsafecell-behavior-details/1560
[2]: https://users.rust-lang.org/t/is-there-a-better-way-to-overload-index-indexmut-for-a-rc-refcell/15591/12

Two phase borrows rewrite

This definitely needs a careful review. Both @pnkfelix and @nikomatsakis  were involved with the design of this so they're natural choices here. I'm r?'ing @pnkfelix since they wrote the original two-phase borrow implementation. Also ping @KiChjang who expressed interest in working on this. I'm going to leave a few comments below pointing out some of the more dangerous changes I made (i.e. what I would like reviewers to pay special attention too.)

r? @pnkfelix

rustbuild: pass datadir to rust-installer

This fixes zsh completion install when $datadir != $prefix/share

test: Forcibly remove MAKEFLAGS in compiletest

When executing run-make tests we run a risk of leaking the `MAKEFLAGS`
environment variable if `./x.py` itself was called from `make` (aka `make check
-j3` as the OSX bots do). We may then leak accidentally fds into the child
process and trick it into thinking it's got a jobserver!

Hopefully addresses [this] spurious failure

[this]: https://github.com/rust-lang/rust/pull/48295#issuecomment-372134717

Update Cargo submodule

Hopefully a routine update...

When executing run-make tests we run a risk of leaking the `MAKEFLAGS`
environment variable if `./x.py` itself was called from `make` (aka `make check
-j3` as the OSX bots do). We may then leak accidentally fds into the child
process and trick it into thinking it's got a jobserver!

Hopefully addresses [this] spurious failure

[this]: https://github.com/rust-lang/rust/pull/48295#issuecomment-372134717

Required moving all fulldeps tests depending on `rand` to different locations as
now there's multiple `rand` crates that can't be implicitly linked against.

Pulls in a redesigned `std::simd` module as well as a replacement for the
`is_target_feature_detected!` macro

Remove ONLY_BUILD and ONLY_BUILD_TARGETS

Primarily removes `ONLY_BUILD` and `ONLY_BUILD_TARGETS`. These aren't actually needed in the new system since we can simply not take the relevant `host` and `target` fields if we don't want to run with them in `Step::make_run`.

This PR also includes a few other commits which generally clean up the state of rustbuild, but are not related to the `Step` changes.

The code for several of the core traits doesn't use hygenic macros.
This isn't a problem, except for the Debug trait, which is the only
one that uses a variable, named "builder".

Variables can't share names with unit structs, so attempting to
[derive(Debug)] on any type while a unit struct with the name
"builder" was in scope would result in an error.

This commit just changes the name of the variable to
"__debug_trait_builder", because I couldn't figure out how to get a
list of all unit structs in-scope from within the derive expansion
function. If someone wants to have a unit struct with
the exact name "__debug_trait_builder", they'll just have to do it
without a [derive(Debug)].

Some minor CI changes

1. On macOS, ensure crash log printing won't error, and only real crash logs are printed. This may avoid the `find` process exiting abnormally and truncated the Travis log (I guess).

2. Print `/proc/cpuinfo` and `/proc/meminfo`. To determine if there's any variation in the reported clock rate between jobs.

travis: Upgrade OSX builders

This upgrades the OSX builders to the `xcode9.3-moar` image which has 3 cores as
opposed to the 2 that our builders currently have. Should help make those OSX
builds a bit speedier!

(Meanwhile, a couple of parse-fail tests are moved to UI tests so that
the reader can see the new output, and an existing UI test is given a
more evocative name.)

Merge LLVM fix for undefined bss globals

This fixes #41315.

r? @japaric

Move PROFQ_CHAN to a Session field

r? @michaelwoerister