The easy parts of RFC 1859.  (Just the trait and the lowering, none of
the error message improvements nor the insta-stable impl for Option.)

Without that flag, LLVM generates unaligned memory access instructions, which are not allowed on ARMv5.

For example, the 'hello world' example from `cargo --new` failed with:
```
$ ./hello
Hello, world!
thread 'main' panicked at 'assertion failed: end <= len', src/libcollections/vec.rs:1113
note: Run with `RUST_BACKTRACE=1` for a backtrace.
```

I traced this error back to the following assembler code in `BufWriter::flush_buf`:
```
    6f44:       e28d0018        add     r0, sp, rust-lang#24
[...]
    6f54:       e280b005        add     fp, r0, rust-lang#5
[...]
    7018:       e5cd001c        strb    r0, [sp, rust-lang#28]
    701c:       e1a0082a        lsr     r0, sl, rust-lang#16
    7020:       03a01001        moveq   r1, #1
    7024:       e5cb0002        strb    r0, [fp, rust-lang#2]
    7028:       e1cba0b0        strh    sl, [fp]
```

Note that `fp` points to `sp + 29`, so the three `str*`-instructions should fill up a 32bit - value at `sp + 28`, which is later used as the value `n` in `Ok(n) => written += n`. This doesn't work on ARMv5 as the `strh` can't write to the unaligned contents of `fp`, so the upper bits of `n` won't get cleared, leading to the assertion failure in Vec::drain.

With `+strict-align`, the code works as expected.

…d consts

Closes rust-lang#41323

Part of rust-lang#42171, in preparation for downgrading the contained `TraitRef` to
only its `substs`.

Rather than (ab)using Debug for outputting the type in plain text use the
alternate format parameter which already does exactly that. This fixes
type parameters for example which would output raw HTML.

Also cleans up adding parens around references to trait objects.

Turn sufficiently old compatibility lints into hard errors

It's been almost 7 months since rust-lang#36894 was merged, so it's time to take the next step.

[breaking-change], needs crater run.

PRs/issues submitted to affected crates:
https://github.com/alexcrichton/ctest/pull/17
Sean1708/rusty-cheddar#55
m-r-r/helianto#3
azdle/virgil#1
rust-locale/rust-locale#24
mneumann/acyclic-network-rs#1
reem/rust-typemap#38

cc https://internals.rust-lang.org/t/moving-forward-on-forward-compatibility-lints/4204
cc rust-lang#34537 rust-lang#36887
Closes rust-lang#36886
Closes rust-lang#36888
Closes rust-lang#36890
Closes rust-lang#36891
Closes rust-lang#36892
r? @nikomatsakis

Lower `?` to `Try` instead of `Carrier`

The easy parts of rust-lang/rfcs#1859, whose FCP completed without further comments.

Just the trait and the lowering -- neither the error message improvements nor the insta-stable impl for Option nor exhaustive docs.

Based on a [github search](https://github.com/search?l=rust&p=1&q=question_mark_carrier&type=Code&utf8=%E2%9C%93), this will break the following:

- https://github.com/pfpacket/rust-9p/blob/00206e34c680198a0ac7c2f066cc2954187d4fac/src/serialize.rs#L38
- https://github.com/peterdelevoryas/bufparse/blob/b1325898f4fc2c67658049196c12da82548af350/src/result.rs#L50

The other results appear to be files from libcore or its tests.  I could also leave Carrier around after stage0 and `impl<T:Carrier> Try for T` if that would be better.

r? @nikomatsakis

Edit: Oh, and it might accidentally improve perf, based on rust-lang#37939 (comment), since `Try::into_result` for `Result` is an obvious no-op, unlike `Carrier::translate`.

…laumeGomez

rustdoc: Cleanup associated const value rendering

Rather than (ab)using Debug for outputting the type in plain text use the
alternate format parameter which already does exactly that. This fixes
type parameters for example which would output raw HTML.

Also cleans up adding parens around references to trait objects.

Upgrade ProjectionTy's Name to a DefId

Part of rust-lang#42171, in preparation for downgrading the contained `TraitRef` to
only its `substs`.

Some inline questions in the diff. Look for `FIXME(tschottdorf)`. These comments
should be addressed before merging.

…, r=Susurrus

New error codes next

Part rust-lang#42229.
To be merged after rust-lang#42264.

cc @Susurrus

Add the RLS to .exe, .msi, and .pkg installers

This directly addresses issue rust-lang#42157, adding the RLS as a non-default component in the mentioned installers. The windows installers appear to have the right functionality added, but I don't have a machine that runs OSX, so it would be great if someone could test whether my .pkg commit adds the RLS correctly. The final commit also fixes some formatting issues I'd noticed while working on the installers, but I don't know if that's within the scope of this PR, so input would be appreciated.

ARMv5 needs +strict-align

Without that flag, LLVM generates unaligned memory access instructions, which are not allowed on ARMv5.

For example, the 'hello world' example from `cargo --new` failed with:
```
$ ./hello
Hello, world!
thread 'main' panicked at 'assertion failed: end <= len', src/libcollections/vec.rs:1113
note: Run with `RUST_BACKTRACE=1` for a backtrace.
```

I traced this error back to the following assembler code in `BufWriter::flush_buf`:
```
    6f44:       e28d0018        add     r0, sp, rust-lang#24
[...]
    6f54:       e280b005        add     fp, r0, rust-lang#5
[...]
    7018:       e5cd001c        strb    r0, [sp, rust-lang#28]
    701c:       e1a0082a        lsr     r0, sl, rust-lang#16
    7020:       03a01001        moveq   r1, #1
    7024:       e5cb0002        strb    r0, [fp, rust-lang#2]
    7028:       e1cba0b0        strh    sl, [fp]
```

Note that `fp` points to `sp + 29`, so the three `str*`-instructions should fill up a 32bit - value at `sp + 28`, which is later used as the value `n` in `Ok(n) => written += n`. This doesn't work on ARMv5 as the `strh` can't write to the unaligned contents of `fp`, so the upper bits of `n` won't get cleared, leading to the assertion failure in Vec::drain.

With `+strict-align`, the code works as expected.

…l, r=nikomatsakis

associated_consts: check trait obligations and regionck for associated consts

Closes rust-lang#41323

r? @nikomatsakis

…recv-timeout-docs, r=QuietMisdreavus

Rewrite doc examples for `Receiver::recv_timeout`.

None