Fix transmute::<T, U> where T requires a bigger alignment than U

For transmute::<T, U> we simply pointercast the destination from a U
pointer to a T pointer, without providing any alignment information,
thus LLVM assumes that the destination is aligned to hold a value of
type T, which is not necessarily true. This can lead to LLVM emitting
machine instructions that assume said alignment, and thus cause aborts.

To fix this, we need to provide the actual alignment to store_operand()
and in turn to store() so they can set the proper alignment information
on the stores and LLVM can emit the proper machine instructions.

Fixes #32947

Avoid rustdoc ICE when an unstable feature is used

Fix #36159.

Don't leak the compiler's internal representation of scopes in error messages.

Fixes #37884 (actually fixes #27942, which was made worse by #37412) by handling more node types.
Ideally we'd turn the unknown node type situations into ICEs and fix them as they show up in errors.
But we might want to backport this patch so I was less aggressive.

Add socket timeout and ttl support in `sys::redox`

This adds support for `read_timeout`, `write_timeout`, and `ttl` on `TcpStream`, `TcpListener`, and `UdpSocket` in the `sys::redox` module.

The DNS lookup has been set to use a 5 second timeout by default.

rustbuild: Fix a few rebuilding issues

Did a bit of investigation and found a few small unrelated issues, but this should help clean up a lot of errors we've been seeing locally.

Use more specific panic message for &str slicing errors

Separate out of bounds errors from character boundary errors, and print
more details for character boundary errors.

It reports the first error it finds in:

1. begin out of bounds
2. end out of bounds
3. begin <= end violated
3. begin not char boundary
5. end not char boundary.

Example:

    &"abcαβγ"[..4]

    thread 'str::test_slice_fail_boundary_1' panicked at 'byte index 4 is not
    a char boundary; it is inside 'α' (bytes 3..5) of `abcαβγ`'

Fixes #38052

Recent versions of Cargo lift less output up into the "main" directory, so let's
look more inside the `deps` folder for changes to propagate differences.

Closes #38744
Closes #38746

Despite what the comment says, we actually need to do this. We're not cleaning
out the stage0 compiler's sysroot, but rather just our own sysroot that we
assembled previously.

prefer hyphens in test files named after issue numbers

We have a lot of tests with filenames honoring particular issues by
number. Typically, these are called issue-${issue_no}.rs (note the
hyphen):

```
$ find . -regextype posix-egrep -regex '.*/issue-[0-9]*.rs' | wc
   1289    1289   35935
```

We also had a much smaller number of files that are like this, but don't
have a hyphen in between the substring `issue` and the number:

```
$ find . -regextype posix-egrep -regex '.*/issue[0-9]*.rs'
./debuginfo/issue14411.rs
./debuginfo/issue12886.rs
./debuginfo/issue13213.rs
./debuginfo/issue22656.rs
./debuginfo/issue7712.rs
./compile-fail/issue32829.rs
./run-pass/issue24353.rs
./run-pass/issue34796.rs
./run-pass/issue18173.rs
./run-pass/issue22346.rs
./run-pass/auxiliary/issue13507.rs
./run-pass/issue26127.rs
./run-pass/issue22008.rs
./run-pass/issue34569.rs
./run-pass/issue29927.rs
./run-pass/issue36260.rs
```

Some would argue that the inconsistency is æsthetically displeasing,
hence this trivial patch. (Note that run-pass/auxiliary/issue13507.rs
has an excuse; it's `use`d in run-pass/issue-13507-2.rs; the matter of
there being two different compile-fail tests with different name
conventions for issue no. 32829 is also neglected here for the sake of
keeping this trivial cleanup patch as trivial as possible for ease of
review.)

Don't warn about dead foreign items if the 'allow(dead_code)' attribute is present

This functionality was missing, and should have existed previously.

Fixes #38780

Reword 'stupid' and 'crazy' in docs.

These terms are not very descriptive and are better reworded as something else.

This functionality was missing, and should have existed previously.

Fixes #38780

Fix debuginfo for unsized struct members

The member was given the size of a fat pointer, which caused
llvm to emit DWARF attributes for a 128-bit bitfield.

Fix pre-cfg_attr notation in comment

Commit aa3b1261 has changed notation
in the test from `#[ignore(cfg(ignorecfg))]` to `#[cfg_attr(ignorecfg, ignore)]`,
but missed to change the comment in the accompanying Makefile.

Stop creating fake HIR pattern nodes.

This replaces all the HIR patterns `rustc_const_eval` creates with the more appropriate HAIR equivalent.

The only place left that creates HIR nodes is the "explicit lifetimes in function signature" suggestion, which only creates type nodes while rebuilding the signature, but that is only in case of an error.

cc @arielb1

Add missing example for Thread struct

r? @frewsxcv

rustbuild: fix dist-analysis with full bootstrap disabled

Really fixes #38734, per discussion in #38752 which was solving the underlying problem the wrong way.

This just mirrors the [similar logic] in documentation building as suggested, that just takes the stage1 compiler artifacts instead in case of non-full-bootstrap builds. Actually copying the artifacts around seems to be unnecessary.

r? @alexcrichton

[similar logic]: https://github.com/rust-lang/rust/blob/7b659cfdbce094a790dbb246da2681a47565782a/src/bootstrap/doc.rs#L140-L144

Commit aa3b1261 has changed notation
in the test from `#[ignore(cfg(ignorecfg))]` to `#[cfg_attr(ignorecfg, ignore)]`,
but missed to change the comment in the accompanying Makefile.

Use `?` instead of `try!` macro in `print::pprust`

Add pretty printing of unions in debuggers

Fixes #37479

Improve naming style in rustllvm.

As per the LLVM style guide, use CamelCase for all locals and classes,
and camelCase for all non-FFI functions.
Also, make names of variables of commonly used types more consistent.

Fixes #38688.

r? @rkruppe

sparc64-linux support

This is built on top of #38656 and depends on rust-lang/libc#483

Hello world works.

The libc-test test suite passes.

`panic!` doesn't fully work:

```
$ qemu-sparc64-static ./panic
thread 'main' panicked at 'explicit panic', panic.rs:1
note: Run with `RUST_BACKTRACE=1` for a backtrace.
Illegal instruction (core dumped)
```

Backtraces don't work either, probably related to the previous point:

```
$ export RUST_BACKTRACE=1
$ qemu-sparc64-static ./panic
thread 'main' panicked at 'explicit panic', panic.rs:1
stack backtrace:
Illegal instruction (core dumped)
```

r? @alexcrichton

@jakllsch Does panicking / backtraces work on sparc64-netbsd?

cc @glaubitz

Fixes #37479

Add links to methods on all slice iterator struct docs

In the same style as `std::slice::Iter` to help people find how to create iterators.

r? @steveklabnik

TrustedLen for Empty and Once.

These implementations were missing, so, I went ahead and added them.

Add a DroplessArena and utilize it as a more efficient arena when possible

I will collect performance (probably just `-Ztime-passes`, and more if that shows significant differences, perhaps).

6feba98 also fixes a potential infinite loop if inplace reallocation failed for `TypedArena` (and `DroplessArena` via copied code).

r? @EddyB

rustbuild: save the save analysis

Fixes #38734. ~~call me the nightly firefighter~~

r? @alexcrichton

Gate on distcheck on Travis

This commit adds a new entry to the Travis matrix to gate on distcheck, the illustrious test process that has historically taken *8 hours* to complete and also breaks all the time on nightly. By adding it to Travis we should hope to never see nightly breakage (like https://github.com/rust-lang/rust/issues/38690) because of this ever again!

"But wait, surely we can't wait 8 hours for all PRs!" you might be thinking, and you are indeed correct. The distcheck added here is much more optimized for speed than the old buildbot instances for a number of reasons:

* We're not building *two host compilers* beforehand. The current distcheck bot does a cross for i686 Linux and x86_64 Linux before it actually runs distcheck, building 6 compilers and LLVM twice. None of this is done in parallel as well (e.g. `-j1`). Not doing any of this work will be a huge win!
* We're using sccache to compile LLVM, so it should be much faster. Distcheck on the bots didn't cache LLVM well and rebuilt it every time.

All in all, this version of "distcheck" should be exactly like other matrix entries that run tests except that it's a *little* slower to start as it has to create the source tarball then rebuild the build system in the distcheck dir. Overall this should be well under the 2 hours that Android is currently taking anyway.

Closes https://github.com/rust-lang/rust/issues/38691