Delete deprecated & unstable range-specific `step_by`

Using the new one is annoying while this one exists, since the inherent method hides the one on iterator.

Tracking issue: #27741
Replacement: #41439
Deprecation: #42310 for 1.19
Fixes #41477

Add .editorconfig to src/rustllvm

... which uses 2 space indent instead of common 4 spaces.

[libstd_unicode] Upgrade to Unicode 10.0.0

Update `libstd_unicode`'s data tables to Unicode 10.0.0, as released on 2017 June 20: http://www.unicode.org/versions/Unicode10.0.0/

Fix Redox build, apparently broken by #42687

Stabilize feature sort_unstable

Closes #40585

Output column number info when panicking

Outputs the column number when panicking. Useful when you e.g. have code like `foo[i] = bar[k] + bar[l]` and you get a panic with index out of bounds, or when you have an expression like `a = b + c + d + e` and the addition overflows. Now you know which operation to blame!

The format is `file:line:column`, just like for compiler errors. Example output with the patch:

```
thread 'main' panicked at 'index out of bounds: the len is 5 but the index is 8', src/main.rs:3:8
```

As some of the API between the compiler and the library landscape gets broken, this is a bit hackier than I'd originally wanted it to be.

* `panic` and `panic_bounds_check` lang items got an additional column param, on stage0 I still have to use the previous version. After a SNAP this should be resolved.
* For `#[derive(RustcDeserialze)]`, stage0 requires a fixed signature for `std::rt::begin_panic`, so we can't change it right away. What we need to do instead is to keep the signature, and add a `begin_panic_new` function that we use in later stages instead. After a SNAP we can change the `begin_panic` function and rely on it instead of `begin_panic_new`, and one SNAP later we can remove `begin_panic_new`.
* Fortunately I didn't have to break anything about the panic hook API, I could easily extend it.

Note that debuginfo remains unchanged, so RUST_BACKTRACE output won't contain any column info. See issue #42921 for discussion on including the column in debuginfo.

... to get https://github.com/rust-lang/cargo/pull/4244 and
https://github.com/rust-lang/cargo/pull/4246

report the total number of errors on compilation failure

Prior to this PR, when we aborted because a "critical pass" failed, we displayed the number of errors from that critical pass. While that's the number of errors that caused compilation to abort in *that place*, that's not what people really want to know. Instead, always report the total number of errors, and don't bother to track the number of errors from the last pass that failed.

This changes the compiler driver API to handle errors more smoothly, therefore is a compiler-api-[breaking-change].

Fixes #42793.

r? @EddyB

Prior to this PR, when we aborted because a "critical pass" failed, we
displayed the number of errors from that critical pass. While that's the
number of errors that caused compilation to abort in *that place*,
that's not what people really want to know. Instead, always report the
total number of errors, and don't bother to track the number of errors
from the last pass that failed.

This changes the compiler driver API to handle errors more smoothly,
and therefore is a compiler-api-[breaking-change].

Fixes #42793.

This reverts commit 5558c64f.

Replacement: 41439
Deprecation: 42310 for 1.19
Fixes 41477

bootstrap: Fix all the pep-8 issues reported by flake8

This commit also adds a few missing docstrings.

Today, after reading this [article](https://blog.rust-lang.org/2017/06/27/Increasing-Rusts-Reach.html), I downloaded this project and started building from source. In the meantime, I began to read the `bootstrap.py`, to know more about the building process, and I made a few changes, this is my first contribution to the project, hope you like it.

BTW, I have a few doubts about the `bootstrap.py`, any guidance is more than welcome:

* Where can I find the unit tests for this script? In case it doesn't exist yet, do you like to include some unit tests with pytest?
* Some methods like `fix_executable`, `get_string`, and `exe_suffix` in the `RustBuild` class should be converted to a function because it doesn't use `self` anywhere. What do you think?

Stabilize 'more_io_inner_methods' feature.

As in the title. Closes #41519.

Improve tests and benchmarks for slice::sort and slice::sort_unstable

This PR just hardens the tests and improves benchmarks.
More specifically:

1. Benchmarks don't generate vectors in `Bencher::iter` loops, but simply clone pregenerated vectors.
2. Benchmark `*_strings` doesn't allocate Strings in `Bencher::iter` loops, but merely clones a `Vec<&str>`.
3. Benchmarks use seeded `XorShiftRng` to be more consistent.
4. Additional tests for `slice::sort` are added, which test sorting on slices with several ascending/descending runs. The implementation identifies such runs so it's a good idea to test that scenario a bit.
5. More checks are added to `run-pass/vector-sort-panic-safe.rs`. Sort algorithms copy elements around a lot (merge sort uses an auxilliary buffer and pdqsort copies the pivot onto the stack before partitioning, then writes it back into the slice). If elements that are being sorted are internally mutable and comparison function mutates them, it is important to make sure that sort algorithms always use the latest "versions" of elements. New checks verify that this is true for both `slice::sort` and `slice::sort_unstable`.

As a side note, all of those improvements were made as part of the parallel sorts PR in Rayon (nikomatsakis/rayon#379) and now I'm backporting them into libcore/libstd.

r? @alexcrichton

Revert "Stabilize RangeArgument"

This reverts commit 143206d5.

From the discussion in #30877 it seems like this is premature.

 rustbuild: set __CARGO_DEFAULT_LIB_METADATA to channel

Also, update the cargo submodule to handle the new value.

When writing LLVM IR output demangled fn name in comments

`--emit=llvm-ir` looks like this now:

```
; <alloc::vec::Vec<T> as core::ops::index::IndexMut<core::ops::range::RangeFull>>::index_mut
; Function Attrs: inlinehint uwtable
define internal { i8*, i64 } @"_ZN106_$LT$alloc..vec..Vec$LT$T$GT$$u20$as$u20$core..ops..index..IndexMut$LT$core..ops..range..RangeFull$GT$$GT$9index_mut17h7f7b576609f30262E"(%"alloc::vec::Vec<u8>"* dereferenceable(24)) unnamed_addr #0 {
start:
  ...
```

cc https://github.com/integer32llc/rust-playground/issues/15

This commit also adds a few missing docstrings

fixed some clippy warnings in compiletest

This is mainly readability stuff. Whenever the `clone_ref` lint asked me to clone the dereferenced object, I removed the `.clone()` instead, relying on the fact that it has worked so far and the immutable borrow ensures that the value won't change.

`--emit=llvm-ir` looks like this now:

```
; <alloc::vec::Vec<T> as core::ops::index::IndexMut<core::ops::range::RangeFull>>::index_mut
; Function Attrs: inlinehint uwtable
define internal { i8*, i64 } @"_ZN106_$LT$alloc..vec..Vec$LT$T$GT$$u20$as$u20$core..ops..index..IndexMut$LT$core..ops..range..RangeFull$GT$$GT$9index_mut17h7f7b576609f30262E"(%"alloc::vec::Vec<u8>"* dereferenceable(24)) unnamed_addr #0 {
start:
  ...
```

cc https://github.com/integer32llc/rust-playground/issues/15