Add E0619 error explanation

r? @EddyB

Document possible `io::ErrorKind`s of `fs::open`

Try to make clear that this isn't an API guarantee for now, as we likely
want to refine these errors in the future, e.g. `ENOSPC` "No space left
on device".

CC #40322

Update RLS submodule

Adding diagnostic code 0611 for lifetime errors with one named, one anonymous lifetime parameter

This is a fix for #42517
Note that this only handles the above case for **function declarations** and **traits**.
`impl items` and `closures` will be handled in a later PR.
Example
```
fn foo<'a>(x: &i32, y: &'a i32) -> &'a i32 {
    if x > y { x } else { y }
}
```
now displays the following error message. ui tests have been added for the same.
```
error[E0611]: explicit lifetime required in the type of `x`
11 | fn foo<'a>(x: &i32, y: &'a i32) -> &'a i32 {
   |                     ^ consider changing the type of `x` to `&'a i32`
12 |     if x > y { x } else { y }
   |                  - lifetime `'a` required
```
#42516
r? @nikomatsakis

Coerce fields to the expected field type

Fully fixes #31260.

This needs a crater run. I was supposed to do this last month but it slipped. Let's get this done.

Add `Iterator::for_each`

This works like a `for` loop in functional style, applying a closure to
every item in the `Iterator`.  It doesn't allow `break`/`continue` like
a `for` loop, nor any other control flow outside the closure, but it may
be a more legible style for tying up the end of a long iterator chain.

This was tried before in #14911, but nobody made the case for using it
with longer iterators.  There was also `Iterator::advance` at that time
which was more capable than `for_each`, but that no longer exists.

The `itertools` crate has `Itertools::foreach` with the same behavior,
but thankfully the names won't collide.  The `rayon` crate also has a
`ParallelIterator::for_each` where simple `for` loops aren't possible.

> I really wish we had `for_each` on seq iterators. Having to use a
> dummy operation is annoying.  - [@nikomatsakis][1]

[1]: https://github.com/nikomatsakis/rayon/pull/367#issuecomment-308455185

Rebase LLVM on top of LLVM 4.0.1

Fixes #42893.

Please don't backport this to beta as-is - I'm not sure I want rust-lang/llvm#84 to sneak to beta before it gets sufficient testing.

r? @alexcrichton

Shift mir-dataflow from `rustc_borrowck` to `rustc_mir` crate.

Shift mir-dataflow from `rustc_borrowck` to `rustc_mir` crate.

Turn `elaborate_drops` and `rustc_peek` implementations into MIR passes that also live in `rustc_mir` crate.

Rewire things so `rustc_driver` uses the `ElaborateDrops` from `rustc_mir` crate.

(This PR is another baby step for mir-borrowck; it is a piece of work that other people want to rebase their stuff on top of, namely developers who are doing other dataflow analyses on top of MIR.)

I have deliberately architected this PR in an attempt to minimize the number of actual code changes. The majority of the diff should be little more than changes to mod and use declarations, as well as a few visibility promotions to pub(crate) when a declaration was moved downward in the module hierarchy.

(I have no problem with other PR's that move declarations around to try to clean this up; my goal was to ensure that the diff here was as small as possible, to make the review nearly trivial.)

Make `$crate` a keyword

Fixes https://github.com/rust-lang/rust/issues/42898

r? @jseyfried or @nrc

Stop disabling fill in jemalloc

The underlying bug has been fixed for over 2 years!

r? @alexcrichton

Unsized tuple coercions

Part of #18469. Fixes #32702.

#37685 and #34451 might also be related.

This PR does the following:

- Introduce explicit `Sized` constraints on tuple initializers, similar to that of record-struct initializers. Not much relevant to the main contribution but I noticed this when making tests for unsized tuple coercions.
- Implement `(.., T): Unsize<(.., U)>` where `T: Unsize<U>`.
- Assume `(.., T)` is MaybeUnsizedUnivariant.
- Modify `src/librustc/ty/util.rs` and `src/librustc_trans/glue.rs` so that tuples and structs are uniformly traversed when translating.

Remove err methods

To be merged after #42519.

cc @Susurrus @QuietMisdreavus

Rollup of 12 pull requests

- Successful merges: #42219, #42831, #42832, #42884, #42886, #42901, #42919, #42920, #42946, #42953, #42955, #42958
- Failed merges: