This tiny patch merely applies @bluss's suggestion for how to get a more
informative error message when the feature check can't open a file, a
matter that had briefly annoyed the present author, leading to the
filing of #38417.

rustbuild: Add sccache support

This commit adds support for sccache, a ccache-like compiler which works on MSVC
and stores results into an S3 bucket. This also switches over all Travis and
AppVeyor automation to using sccache to ensure a shared and unified cache over
time which can be shared across builders.

The support for sccache manifests as a new `--enable-sccache` option which
instructs us to configure LLVM differently to use a 'sccache' binary instead of
a 'ccache' binary. All docker images for Travis builds are updated to download
Mozilla's tooltool builds of sccache onto various containers and systems.
Additionally a new `rust-lang-ci-sccache` bucket is configured to hold all of
our ccache goodies.

---

Note that this does not currently change Windows [due to previously written up issues](https://github.com/rust-lang/rust/issues/38119#issuecomment-266631585). Despite that, however, I was curious to get timings for the builds on Travis to see what ranges we're working with. As a result, this is a WIP PR I'm using to gauge build times and such.

make deterministic_hash host-architecture-independent

`DefPath::deterministic_hash` used to call `std::hash::Hash`, which depends on the current architecture in several ways, which would prevent metadata written on one host architecture from being successfully read on another one.

Use a hasher we control instead.

Fixes #38177.

r? @michaelwoerister

Fix unaligned loads in librustc_metadata

Creating a `&[u32]` from an `&[u8]` is not necessarily valid, and crashes
on certain platforms if the data is not well aligned.

rustbuild: Package rust-mingw by default

This fixes the `make dist` step on MinGW to package the `rust-mingw` component
by default. This should hopefully be the last step in fixing nightlies.

The standard implementations of Hasher have architecture-dependent
results when hashing integers. This causes problems when the hashes are
stored within metadata - metadata written by one host architecture can't
be read by another.

To fix that, implement an architecture-independent StableHasher and use
it in all places an architecture-independent hasher is needed.

Fixes #38177.

This fixes the `make dist` step on MinGW to package the `rust-mingw` component
by default. This should hopefully be the last step in fixing nightlies.

rustbuild: Add cli option --keep-stage

This option is intended to be used like:

./x.py build --stage 1 --keep-stage 0

Which skips all stage 0 steps, so that stage 1 can be recompiled
directly (even if for example libcore has changes).

This is useful when working on `cfg(not(stage0))` parts of the
libraries or when re-running stage 1 tests in libraries in general.

Fixes #38326

libtest: add --list option to list tests and benchmarks

This option lists all the tests and benchmarks a binary provides without running any of them.
By default the listing is sent to stdout (intended for human consumption), but if `--logfile` is also specified, it is also written there in an easily parsable form.

If filters are specified, they're applied before the output is emitted. The human output will also include a summary unless `-q` is specified.

Redox Support Preview

# Important - This is only a preview of a working `sys::redox`.

Compiling the Redox default distribution with this `libstd` results in a fully functioning distribution. As such, all further changes would be cosmetic or implementing features that have not been used by the default distribution (of which there are only a small number).

I do not expect this to be merged, but would like to discuss how it may be improved and get feedback.

There are a few `unimplemented!()` - `cloexec` for example. I have documented them below. These would be resolved before desiring a merge.

There are also issues with how the Redox syscall library is called - currently I am using a re-export in `libc` but that probably would not be desired.

Fix regression in resolution of primitive types

Fix often encountered ICE.
Extracted from https://github.com/rust-lang/rust/pull/38154
Fixes https://github.com/rust-lang/rust/issues/38155, fixes https://github.com/rust-lang/rust/issues/38188, fixes https://github.com/rust-lang/rust/issues/38277, fixes https://github.com/rust-lang/rust/issues/38280, fixes https://github.com/rust-lang/rust/issues/38292, fixes https://github.com/rust-lang/rust/issues/38311, fixes https://github.com/rust-lang/rust/issues/38344, fixes https://github.com/rust-lang/rust/issues/38363, fixes https://github.com/rust-lang/rust/issues/38372 (duplicates)

r? @jseyfried or @EddyB or @nrc

This commit adds support for sccache, a ccache-like compiler which works on MSVC
and stores results into an S3 bucket. This also switches over all Travis and
AppVeyor automation to using sccache to ensure a shared and unified cache over
time which can be shared across builders.

The support for sccache manifests as a new `--enable-sccache` option which
instructs us to configure LLVM differently to use a 'sccache' binary instead of
a 'ccache' binary. All docker images for Travis builds are updated to download
Mozilla's tooltool builds of sccache onto various containers and systems.
Additionally a new `rust-lang-ci-sccache` bucket is configured to hold all of
our ccache goodies.

mk: Fix `make check`

When the rustc-unicode crate was renamed to std-unicode we just need to continue
to filter it out of the crates being tested.

When the rustc-unicode crate was renamed to std-unicode we just need to continue
to filter it out of the crates being tested.

rustbuild: Run `dist` on a `distcheck`

This is what the nightly bots expect, so let's be sure to do that.

This is what the nightly bots expect, so let's be sure to do that.

This option lists all the tests and benchmarks a binary provides. By default the listing
is sent to stdout, but if --logfile is also specified, it is written there.

If filters are specified, they're applied before the output is emitted.

[LLVM 4.0] Update LLVM global variable debug info API for 4.0

This teaches Rust about an LLVM 4.0 API change for creating debug info
for global variables.

This change was made in upstream LLVM patch https://reviews.llvm.org/D20147

This is almost a 1:1 copy of how clang did it in http://reviews.llvm.org/D20415

Document --test-args for rustbuild

There are three changes:

* Replace --filter with --test-args
* Delete `./x.py test src/test/run-pass/assert-*` example, which doesn't work
* As driveby, update Buildbot URLs to https

Fix #38275.

r? @alexcrichton

Fix travis builds

After reading some articles [1] [2] yesterday about Docker and the "init"
process I got to thinking about the problems that we've been seeing on Travis.
The basic problem is that a Linux system may need an "init" process to work
properly when processes become zombies. Docker by default doesn't handle this
and the root process typically isn't an init process, so this can occasionally
cause quite a few problems.

We've been seeing spurious errors on Travis inside containers which look like
OOM and such, but my guess is that zombie processes were being reparented to the
top-level shell. The shell didn't expect the zombies and then behaved very
strangely.

This commit fixes these problems by using Yelp's "dumb-init" program [2] as the
init process in all of our containers. This ensures that there's a valid init
ready to reap children when they're reparented, which our test suite apparently
generates a bunch of throughout the tests and such.

[1]: https://blog.phusion.nl/2015/01/20/docker-and-the-pid-1-zombie-reaping-problem/
[2]: https://engineeringblog.yelp.com/2016/01/dumb-init-an-init-for-docker.html

This teaches Rust about an LLVM 4.0 API change for creating debug info
for global variables.

This change was made in upstream LLVM patch https://reviews.llvm.org/D20147

This is almost 1:1 copy of how clang did it in http://reviews.llvm.org/D20415

Allow copy-propagation of function arguments

Allow propagating function argument locals in copy propagation.

libtest: add --exact to make filter matching exact

Filter matching is by substring by default. This makes it impossible
to run a single test if its name is a substring of some other test.
For example, its not possible to run just `mymod::test` with these
tests:

```
  mymod::test
  mymod::test1
  mymod::test_module::moretests
```

You could declare by convention that no test has a name that's a
substring of another test, but that's not really practical.

This PR adds the `--exact` flag, to make filter matching exactly
match the complete name.

Creating a `&[u32]` from a `&[u8]` was not valid; the data is not
necessarily well aligned.

Improve proc-macro def ids

Support `cstore.relative_def_path(id)` and `cstore.def_key(id)` with proc-macro def ids.
Fixes #38207.
r? @nikomatsakis

Another round of nightly fixes

Another three separate errors happened last night:

* Race condition in save analysis failed the OX build
* Packaging docs that don't exist failed the Android build
* Packaging save-analysis that doesn't exist failed the cross host builds

It just never ends...

This commit skips the `docs` dist step if the `--disable-docs` flag is passed,
fixing a compile error seen on nightly.

This commit skips a few more dist tragets during compilation which shouldn't be
necessary.

* First, when packaging std we only take action when the host target is the
  build target. Otherwise we package the same artifacts a number of times, which
  shouldn't be necessary.
* Next, we apply the same logic to the save-analysis build. This is actually
  required for correctness as the build compiler is the only one which actually
  has save analysis information. This should fix an error seen on nightlies.

The OSX bots failed last night due a race condition in save analysis where
concurrent calls to `fs::create_dir_all` conflicted with one another. This
replaces the relevant function call with `fs::create_dir_racy` which is defined
internally to the compiler.

[LLVM 4.0] Move debuginfo alignment argument

Alignment was removed from createBasicType and moved to

- createGlobalVariable
- createAutoVariable
- createStaticMemberType (unused in Rust)
- createTempGlobalVariableFwdDecl (unused in Rust)

https://github.com/llvm-mirror/llvm/commit/e69c459a6e9756ca1ff3acb1dcfc434843aee80f

Implement RFC #1725 (read_unaligned, write_unaligned)

cc #37955

r? @alexcrichton

[MSP430] Do not generate '@' character in symbol names.

MSP430 assembler does not like '@' character in symbol names, so we need
to replace it with some other character.

Fixes #38116

After reading some articles [1] [2] yesterday about Docker and the "init"
process I got to thinking about the problems that we've been seeing on Travis.
The basic problem is that a Linux system may need an "init" process to work
properly when processes become zombies. Docker by default doesn't handle this
and the root process typically isn't an init process, so this can occasionally
cause quite a few problems.

We've been seeing spurious errors on Travis inside containers which look like
OOM and such, but my guess is that zombie processes were being reparented to the
top-level shell. The shell didn't expect the zombies and then behaved very
strangely.

This commit fixes these problems by using Yelp's "dumb-init" program [2] as the
init process in all of our containers. This ensures that there's a valid init
ready to reap children when they're reparented, which our test suite apparently
generates a bunch of throughout the tests and such.

[1]: https://blog.phusion.nl/2015/01/20/docker-and-the-pid-1-zombie-reaping-problem/
[2]: https://engineeringblog.yelp.com/2016/01/dumb-init-an-init-for-docker.html

feat(rustdoc): harmonise error messages

Based on unix tools wording, it follows a standard format: `program_name: context: error message`, potentially prompting the user to use the `--help` option.

This is clearly meant to trigger some discussion on #38084, as messages still use `stdout` and `stderr` somewhat arbitrarily, and there are a few `error!()` calls as well.

cc #37955

Rollup of 7 pull requests

- Successful merges: #37052, #37941, #38067, #38164, #38202, #38264, #38299
- Failed merges: