Add missing urls for Mutex

r? @rust-lang/docs

Typo in `librustc/README.md`

Use HTTPS protocol for "chat.mibbit.com"

I changed the `http://` protocol to `https://` for the `chat.mibbit.com` website. 📝

--[**Suriyaa**](https://mozillians.org/de/u/suriyaakudo/) 🦊

(*PS: Is somebody interested to vouch me at https://mozillians.org/de/u/suriyaakudo/?*)

`EndRegion` do not always correspond to borrow-data entries

Remove assertion that the argument to every `EndRegion` correspond to some dataflow-tracked borrow-data entry.

Fix #44828

(The comment thread on the aforementioned issue discusses why its best to just remove this assertion.)

update books for next release

Also fixes some stdlib links to the reference which have changed.

First step in https://forge.rust-lang.org/release-process.html, doing it a few days early 😄

fix ItemKind::DefaultImpl doc comment

Upgrade comment to doc comment.

...Is this actually used? If so, why does the `Impl` variant right below have a `Defaultness`?

Add links to headers in README and CONTRIBUTING

this also adds dependencies to CONTRIBUTING

I'm just getting started building the rust compiler and noticed this information/ability was missing.

It was also missing the gdb dependency for running tests. I pulled the information out of `appveyor.yml` and recommended later than 7.1 because that is what [apt ships](https://packages.ubuntu.com/search?suite=trusty&keywords=gdb). Feel free to tell me something different!

Corrected the CONTRIBUTING.md "External Dependencies" section

The "External Dependencies" section is a little outdated.
Please see following comments https://github.com/rust-lang/rust/pull/44567#issuecomment-329797331 https://github.com/rust-lang/rust/pull/44567#issuecomment-329799655 for rationale.

Don't use remapped path when loading modules and include files

Fixes bug reported in https://github.com/rust-lang/rust/issues/41555#issuecomment-327866056.

cc @michaelwoerister

Updated RELEASES.md for 1.21.0

[Rendered](https://github.com/Aaronepower/rust/blob/master/RELEASES.md)

incr.comp.: Switch to red/green change tracking, remove legacy system.

This PR finally switches incremental compilation to [red/green tracking](https://github.com/rust-lang/rust/issues/42293) and completely removes the legacy dependency graph implementation -- which includes a few quite costly passes that are simply not needed with the new system anymore.

There's still some documentation to be done and there's certainly still lots of optimizing and tuning ahead -- but the foundation for red/green is in place with this PR. This has been in the making for a long time `:)`

r? @nikomatsakis
cc @alexcrichton, @rust-lang/compiler

Remove mem::transmute used in Box<str> conversions

Given that https://github.com/rust-lang/rust/pull/44877 is failing, I decided to make a separate PR. This is done with the same motivation: to avoid `mem::transmute`-ing non `#[repr(C)]` types.

add notes to report_conflicting_borrow MIR borrowck

part of #44596

Update docs for process::abort

Remove a typo and explain the relationship to `panic!`.

Part of #29370

r? @steveklabnik

Overlapping borrows can point to different lvalues.

Overlapping borrows can point to different lvalues.

There's always a basis for the overlap, so instead of removing the assert entirely, I instead pass in the prefix that we found and check that it actually is a prefix of both lvalues.

Fix #44829

make `backtrace = false` compile for windows targets.

when building for windows with `backtrace = false`, `libstd` fails to compile because some modules that use items from `sys_common::backtrace::*` are still included, even though those modules aren't used or referenced by anything.

`sys_common::backtrace` doesn't exist when the backtrace feature is turned off.

--

i've also added `#[cfg(feature = "backtrace")]` to various items that exist exclusively to support `mod backtrace` since the compilation would fail since they would be unused in a configuration with backtraces turned off.

Made `fs::copy` return the length of the main stream

On Windows with the NTFS filesystem, `fs::copy` would return the sum of the
lengths of all streams, which can be different from the length reported by
`metadata` and thus confusing for users unaware of this NTFS peculiarity.

This makes `fs::copy` return the same length `metadata` reports which is the
value it used to return before PR #26751. Note that alternate streams are still
copied; their length is just not included in the returned value.

This change relies on the assumption that the stream with index 1 is always the
main stream in the `CopyFileEx` callback. I could not find any official
document confirming this but empirical testing has shown this to be true,
regardless of whether the alternate stream is created before or after the main
stream.

Resolves #44532

let htmldocck.py check for directories

Since i messed this up during https://github.com/rust-lang/rust/pull/44613, i wanted to codify this into the rustdoc tests to make sure that doesn't happen again.

MIR borrowck: move span_label to `borrowck_errors.rs`

The calls to `span_label` are moved and factorized for:
* E0503 (`cannot_use_when_mutably_borrowed()`)
* E0506 (`cannot_assign_to_borrowed()`)

Additionnally, the error E0594 (`cannot_assign_static()`) has been factorized between `check_loan.rs` and `borrowc_check.rs`.

Part of #44596

Move monomorphize::resolve() to librustc

this moves `monomorphize::resolve(..)` to librustc, and re-enables inlining for some trait methods, fixing #44389

@nikomatsakis I've kept the calls to the new `ty::Instance::resolve(....)` always `.unwrap()`-ing for the moment, how/do you want to add more debugging info via `.unwrap_or()` or something like this?

we still have some related `resolve_*` functions on monomorphize, but I wasn't sure moving them was into the scope for this PR too.

@EddyB mind to take a look too?

There's always a basis for the overlap, so instead of removing the
assert entirely, I instead pass in the prefix that we found and check
that it actually is a prefix of both lvalues.

Fix #44829

 rustdoc: Render [src] links for trait implementors

Should close #43893.

<s>No tests [yet].</s>

r? @QuietMisdreavus

make non_snake_case lint allow extern no-mangle functions

Resolves #31924.

r? @sfackler

update mdbook

Fixes #44704

some dataflow-tracked borrow-data entry.

Fix #44828

(The comment thread on the aforementioned issue discusses why its best
to just remove this assertion.)

More Altivec Intrinsics

Float-specific intrinsics

Also fixes some stdlib links to the reference which have changed.

Fixes #44704