rustbuild: Implement `make dist`

This commit implements the `make dist` command in the new rustbuild build
system, porting over `dist.mk` and `prepare.mk` into Rust. There's a huge amount
of complexity between those two files, not all of which is likely justified, so
the Rust implementation is *much* smaller.

Currently the implementation still shells out to rust-installer as well as some
python scripts, but ideally we'd rewrite it all in the future to not shell out
and be in Rust proper.

const eval: don't assume the rhs of a bitshift is of any particular type

[regression found](https://internals.rust-lang.org/t/regression-report-stable-2016-03-03-vs-nightly-2016-03-15/3250) in jpeg-decoder

This commit implements the `make dist` command in the new rustbuild build
system, porting over `dist.mk` and `prepare.mk` into Rust. There's a huge amount
of complexity between those two files, not all of which is likely justified, so
the Rust implementation is *much* smaller.

Currently the implementation still shells out to rust-installer as well as some
python scripts, but ideally we'd rewrite it all in the future to not shell out
and be in Rust proper.

Resolve: improve diagnostics for duplicate definitions and imports

This PR improves and regularizes the diagnostics for duplicate definitions and imports.

After this PR, the second of two duplicate definitions/imports will have the following form:
> a(n) [value|type|module|trait|extern crate] named \`*name*\` has already been [defined|imported] in this [module|block|trait|enum]

with a note referencing this first of the two duplicate definitions/imports:
> previous [definition|import] of \`*name*\` here

The error indices remain unchanged.

r? @EddyB

syntax: Always pretty print a newline after doc comments

Before this patch, code that had a doc comment as the first
line, as in:

```rust
/// Foo
struct Foo;
```

Was pretty printed into:

```rust
///Foostruct Foo;
```

This makes sure that that there is always a trailing newline
after a doc comment.

Closes #31722

Normalize return type when checking for E0269

Fixes #31597

First time dealing with normalization. Maybe `normalize_associated_type` would be better here, but it seems to imply it's only used during trans.

update compiler-rt submodule

fixes #32194

also see rust-lang/compiler-rt#17

r? @alexcrichton

Fixes #31597

std: Fix overflow when subtracting Instant

This code was currently only exercised on OSX, but this applies the same method
of subtraction used on Linux which doesn't have the same overflow issues.

Note that this currently includes no tests, but that's because this is only
visible with debug assertions enabled. Soon, however, I'll enable debug
assertions on all auto builds on the bots so we should get testing for this.

Closes #32268

rustbuild: Fix LLVM compile on MinGW

The LLVM change [1] in #32239 unfortunately broke the LLVM build on MinGW, so
this LLVM submodule update brings in one more fix [2] which should hopefully
remedy that.

Once this lands we should be able to immediately start gating on this to prevent
it from happening again.

[1]: https://github.com/rust-lang/llvm/commit/be89e4b5
[2]: https://github.com/rust-lang/llvm/commit/3dcd2c84

fixes #32194

rustc: Improve compile time of platform intrinsics

This commit improves the compile time of `rustc_platform_intrinsics` from 23s to
3.6s if compiling with `-O` and from 77s to 17s if compiling with `-O -g`. The
compiled rlib size also drops from 3.1M to 1.2M.

The wins here were gained by removing the destructors associated with `Type` by
removing the internal `Box` and `Vec` indirections. These destructors meant that
a lot of landing pads and extra code were generated to manage the runtime
representations. Instead everything can basically be statically computed and
shoved into rodata, so all we need is a giant string compare to lookup what's
what.

Closes #28273

This commit improves the compile time of `rustc_platform_intrinsics` from 23s to
3.6s if compiling with `-O` and from 77s to 17s if compiling with `-O -g`. The
compiled rlib size also drops from 3.1M to 1.2M.

The wins here were gained by removing the destructors associated with `Type` by
removing the internal `Box` and `Vec` indirections. These destructors meant that
a lot of landing pads and extra code were generated to manage the runtime
representations. Instead everything can basically be statically computed and
shoved into rodata, so all we need is a giant string compare to lookup what's
what.

Closes #28273

This code was currently only exercised on OSX, but this applies the same method
of subtraction used on Linux which doesn't have the same overflow issues.

Note that this currently includes no tests, but that's because this is only
visible with debug assertions enabled. Soon, however, I'll enable debug
assertions on all auto builds on the bots so we should get testing for this.

Closes #32268

Refactor rustc_trans::save to allow other backends than CSV

r? @nrc

Things done:
* Moved `(.*)Data` structs to an own module, so they can be imported easily (`use data::*`).
* Created a `Dump` trait with callbacks for dumping items.
* Refactored `DumpCsvVisitor` to use an implementor of `Dump` instead of dumping as CSV. Renamed it to `DumpVisitor`.
* Created a `DumpCsv` struct that implements `Dump` and serializes items as CSV.

I tried to extract some of the logic contained in `FmtStr` and `Recorder`, such as normalization of ids (I put it in `DumpVisitor`). I think it makes sense to provide the same information to other implementors of `Dump`, instead of normalizing only for `DumpCsv`. However, there is still some logic related to spans implemented only for `DumpCsv`. I just thought it would be better to merge this as soon as possible, since there are so much changes, and fix this afterwards.

Move rustc_trans::*Data to own module
Add new data to rustc_trans::save
Create a Dump trait implemented by structs that dump save analysis data
Split dump_csv into a DumpVisitor and a CsvDumper

The LLVM change [1] in #32239 unfortunately broke the LLVM build on MinGW, so
this LLVM submodule update brings in one more fix [2] which should hopefully
remedy that.

Once this lands we should be able to immediately start gating on this to prevent
it from happening again.

[1]: https://github.com/rust-lang/llvm/commit/be89e4b5
[2]: https://github.com/rust-lang/llvm/commit/3dcd2c84

Shorter output for `rustc --test` binaries.

Until now, a program created with `rustc --test` prints at least one line per test. This can be very verbose, especially with [data-driven tests](https://internals.rust-lang.org/t/test-and-external-test-harnesses/3145) when hundreds or thousands of tests is not rare.

This changes the default output to one character per test (except metrics and benchmarks results which have additional data to show):

```
     Running target/debug/wpt-75c594dc1e6e6187

running 314 tests
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..
test result: ok. 314 passed; 0 failed; 0 ignored; 0 measured
```

<s>The previous behavior is available by passing `--verbose` to the test program. Maybe `cargo test --verbose` could be changed to do that?</s> **Edit:** the default is now unchanged, `-q` or `--quiet` enables the new output.

A program created with `rustc --test` prints at least one line per test.
This can be very verbose, especially with [data-driven tests](
https://internals.rust-lang.org/t/test-and-external-test-harnesses/3145)
when hundreds or thousands of tests is not rare.

This adds a `-q` or `--quiet` option that changes the output
to one character instead of one line per test
(except metrics and benchmarks results which have additional data to
show):

```
     Running target/debug/wpt-75c594dc1e6e6187

running 314 tests
..............................................................................
..............................................................................
..............................................................................
..............................................................................
..
test result: ok. 314 passed; 0 failed; 0 ignored; 0 measured
```

This is a breaking change since the `test::TestOpts` struct
now has one more field.

derive: clean up hygiene

derive: clean up hygiene

Fixes #2810.

Spawned from #32139.

r? @alexcrichton

derive: use intrinsics::unreachable over unreachable!()

derive: use intrinsics::unreachable over unreachable!()

Fixes #31574.

Spawned from #32139.

r? @alexcrichton

rustbuild: Fix cross compiling to FreeBSD

This commit fixes our support for cross compiling a compiler to run on FreeBSD.
Over the weekend I managed to get a cross compiler from Linux to FreeBSD [1]
which I hope to soon use to start producing FreeBSD nightly compilers. With the
`make dist` support added in #32237 we should be able to produce standard
rustc/rust-std packages for FreeBSD through a new slave with this cross compiler.

Currently, however, we don't "Just Work" when cross compiling FreeBSD and a
number of changes were required (part of this PR). They include:

* A few build fixes were needed in LLVM. Our own branch has been rebased on the
  actual 3.8 release and I applied one extra commit [2] which contains two fixes:

  1. The LLVM CMake build system passes the `-Wl,-z,defs` flag on many
     platforms, but *not* when `CMAKE_SYSTEM_NAME` is "FreeBSD". Unfortunately
     this doesn't take into account when we're cross compiling, and as predicted
     the build will fail if `-Wl,-z,defs` is passed (see [3] for more info). To
     fix this we test `TARGET_TRIPLE` instead of the `CMAKE_SYSTEM_NAME` which
     is what we're compiling for which fixes the problem.
  2. The `PATH_MAX` constant is apparently defined in a different location than
     many other Unix systems, so a file which required this just needed some
     help to keep compiling.

* Support for compiling compiler-rt with CMake has been added to rustbuild. It
  looks like it just emulates Linux in what it compiles as it didn't seem to
  naturally produce anything else... At least the architecture is right, so
  seems good for now at least!

[1]: https://github.com/alexcrichton/port-of-rust/blob/master/prebuilt/freebsd/Dockerfile
[2]: https://github.com/rust-lang/llvm/commit/be89e4b5
[3]: https://bugs.webkit.org/show_bug.cgi?id=138420

Utilize `Option::cloned` over explicit `clone` usage.

Fix Windows rustbuild

These commits fix the rustbuild Windows bots, namely:

* The 32-bit build of LLVM was failing because libraries weren't being linked. This was in turn caused by the build script for `rustc_llvm` erroneously detecting that it was cross compiling when it actually wasn't.
* Tools of the build were compiled against the wrong libraries, so running them would fail on Windows as rpath didn't exist and `PATH` was wrong.
* Some linkchecker fixes for Windows paths had to be applied as well.

Implement RFC 1210: impl specialization

This PR implements [impl specialization](https://github.com/rust-lang/rfcs/pull/1210),
carefully following the proposal laid out in the RFC.

The implementation covers the bulk of the RFC. The remaining gaps I know of are:

- no checking for lifetime-dependent specialization (a soundness hole);
- no `default impl` yet;
- no support for `default` with associated consts;

I plan to cover these gaps in follow-up PRs, as per @nikomatsakis's preference.

The basic strategy is to build up a *specialization graph* during
coherence checking. Insertion into the graph locates the right place
to put an impl in the specialization hierarchy; if there is no right
place (due to partial overlap but no containment), you get an overlap
error. Specialization is consulted when selecting an impl (of course),
and the graph is consulted when propagating defaults down the
specialization hierarchy.

You might expect that the specialization graph would be used during
selection -- i.e., when actually performing specialization. This is
not done for two reasons:

- It's merely an optimization: given a set of candidates that apply,
  we can determine the most specialized one by comparing them directly
  for specialization, rather than consulting the graph. Given that we
  also cache the results of selection, the benefit of this
  optimization is questionable.

- To build the specialization graph in the first place, we need to use
  selection (because we need to determine whether one impl specializes
  another). Dealing with this reentrancy would require some additional
  mode switch for selection. Given that there seems to be no strong
  reason to use the graph anyway, we stick with a simpler approach in
  selection, and use the graph only for propagating default
  implementations.

Trait impl selection can succeed even when multiple impls can apply,
as long as they are part of the same specialization family. In that
case, it returns a *single* impl on success -- this is the most
specialized impl *known* to apply. However, if there are any inference
variables in play, the returned impl may not be the actual impl we
will use at trans time. Thus, we take special care to avoid projecting
associated types unless either (1) the associated type does not use
`default` and thus cannot be overridden or (2) all input types are
known concretely.

r? @nikomatsakis

This commit fixes our support for cross compiling a compiler to run on FreeBSD.
Over the weekend I managed to get a cross compiler from Linux to FreeBSD [1]
which I hope to soon use to start producing FreeBSD nightly compilers. With the
`make dist` support added in #32237 we should be able to produce standard
rustc/rust-std packages for FreeBSD through a new slave with this cross compiler.

Currently, however, we don't "Just Work" when cross compiling FreeBSD and a
number of changes were required (part of this PR). They include:

* A few build fixes were needed in LLVM. Our own branch has been rebased on the
  actual 3.8 release and I applied one extra commit [2] which contains two fixes:

  1. The LLVM CMake build system passes the `-Wl,-z,defs` flag on many
     platforms, but *not* when `CMAKE_SYSTEM_NAME` is "FreeBSD". Unfortunately
     this doesn't take into account when we're cross compiling, and as predicted
     the build will fail if `-Wl,-z,defs` is passed (see [3] for more info). To
     fix this we test `TARGET_TRIPLE` instead of the `CMAKE_SYSTEM_NAME` which
     is what we're compiling for which fixes the problem.
  2. The `PATH_MAX` constant is apparently defined in a different location than
     many other Unix systems, so a file which required this just needed some
     help to keep compiling.

* Support for compiling compiler-rt with CMake has been added to rustbuild. It
  looks like it just emulates Linux in what it compiles as it didn't seem to
  naturally produce anything else... At least the architecture is right, so
  seems good for now at least!

[1]: https://github.com/alexcrichton/port-of-rust/blob/master/prebuilt/freebsd/Dockerfile
[2]: https://github.com/rust-lang/llvm/commit/be89e4b5
[3]: https://bugs.webkit.org/show_bug.cgi?id=138420