LLVM upgrade

As discussed in https://internals.rust-lang.org/t/need-help-with-emscripten-port/3154/46 I'm trying to update the used LLVM checkout in Rust.

I basically took @shepmaster's code and applied it on top (though I did the commits manually, the [original commits have better descriptions](https://github.com/rust-lang/rust/compare/master...avr-rust:avr-support).

With these changes I was able to build rustc. `make check` throws one last error on `run-pass/issue-28950.rs`. Output: https://gist.github.com/badboy/bcdd3bbde260860b6159aa49070a9052

I took the metadata changes as is and they seem to work, though it now uses the module in another step. I'm not sure if this is the best and correct way.

Things to do:

* [x] ~~Make `run-pass/issue-28950.rs` pass~~ unrelated
* [x] Find out how the `PositionIndependentExecutable` setting is now used
* [x] Is the `llvm::legacy` still the right way to do these things?

cc @brson @alexcrichton

trans: Avoid weak linkage for closures when linking with MinGW.

This PR proposes one possible solution to #34793, the problem that prevents https://github.com/servo/servo/pull/12393 from landing. It applies the same strategy, that we already use for monomorphizations, to closures, that is, instead of emitting symbols with `weak_odr` linkage in order to avoid symbol conflicts, we emit them with `internal` linkage, with the side effect that we have to copy code instead of just linking to it, if more than one codegen unit is involved.
With this PR, the compiler will only apply this strategy for targets where we would actually run into a problem when using `weak_odr` linkage, in other words nothing will change for platforms except for MinGW.

The solution implemented here has one restriction that could be lifted with some more effort, but it does not seem to be worth the trouble since it will go away once we use only MIR-trans: If someone compiles code

1. on MinGW,
2. with more than one codegen unit,
3. *not* using MIR-trans,
4. and runs into a closure inlined from another crate

then the compiler will abort and suggest to compile either with just one codegen unit or `-Zorbit`.

What's nice about this is that I lays a foundation for also doing the same for generics: using weak linkage where possible and thus enabling some more space optimizations that the linker can do.

~~This PR also contains a test case for compiling a program that contains more than 2^15 closures. It's a huge, generated file with almost 100K LOCs. I did not commit the script for generating the file but could do so. Alternatively, maybe someone wants to come up with a way of doing this with macros.~~
The test file is implemented via macros now (thanks @alexcrichton!)

Opinions?

Fixes #34793.

cc @rust-lang/compiler

@tmiasko did some digging and discovered that
https://reviews.llvm.org/D22858 may be relevant.

Suppress unused type parameter error when type has error field

Fix #35075.

Add libarena from local rust to stage0

This was needed at least when local rust was 1.9.0 on darwin.

Fixes #35149

This was needed at least when local rust was 1.9.0 on darwin.

Fixes #35149

typeck: use a TypeVisitor in ctp

Use a TypeVisitor in ctp instead of `ty::walk`

This fixes a few cases where a region could be projected out of a trait while not being constrained by the type parameters, violating rust-lang/rfcs#447 and breaking soundness. As such, this is a [breaking-change].

Fixes #35139

r? @EddyB

Fixes #35139

Avoid writing a temporary closure kind

We used to write a temporary closure kind into the inference table, but
this could lead to obligations being incorrectled resolved before
inference had completed. This result could then be cached, leading to
further trouble. This patch avoids writing any closure kind until the
computation is complete.

Fixes #34349.

r? @arielb1 -- what do you think?

diagnostically note source of overruling outer forbid

When we emit E0453 (lint level attribute overruled by outer `forbid`
lint level), it could be helpful to note where the `forbid` level was
set, for the convenience of users who, e.g., believe that the correct
fix is to weaken the `forbid` to `deny`.

![forbidden_on_whose_authority](https://cloud.githubusercontent.com/assets/1076988/15995312/2d847376-30ce-11e6-865e-b68cfebc0291.png)

Suggest use of `--print target-list` when target is not found.

If given target could not be found suggest using `--print target-list`.
Previously, error has been reported as:

$ rustc --target 86-unknown-linux-gnu
error: Error loading target specification: Could not find specification for target "86-unknown-linux-gnu"

After changes it looks as follows:

$ rustc --target 86-unknown-linux-gnu
error: Error loading target specification: Could not find specification for target "x86-unknown-linux-gnu". Use `--print target-list` for a list of supported targets

If given target could not be found suggest using `--print target-list`.
Previously, error has been reported as:

$ rustc --target x86-unknown-linux-gnu
error: Error loading target specification: Could not find specification for target "x86-unknown-linux-gnu"

After changes it looks as follows:

rustc --target x86-unknown-linux-gnu
error: Error loading target specification: Could not find specification for target "x86-unknown-linux-gnu"
help: Use `--print target-list` for a list of built-in targets

Add ARM MUSL targets

Rebase of #33189.

I tested this by producing a std for `arm-unknown-linux-musleabi` then I cross compiled Hello world to said target. Checked that the produced binary was statically linked and verified that the binary worked under QEMU.

This depends on rust-lang/libc#341. I'll have to update this PR after that libc PR is merged.

I'm also working on generating ARM musl cross toolchain via crosstool-ng. Once I verified those work, I'll send a PR to rust-buildbot.

r? @alexcrichton
cc @timonvo

Fix build of compiler-rt on FreeBSD

Broken since ee6011fc removed cmake from the
process.  There are likely other platforms still broken, but I didn't test on them.

Properly feature gate all unstable ABIs

Fixes https://github.com/rust-lang/rust/issues/34900
[breaking-change]
r? @pnkfelix

---
Function-visiting machinery for AST/HIR is surprisingly error-prone, it's *very* easy to miss some cases or visit something twice while writing a visitor. This is the true problem behind https://github.com/rust-lang/rust/issues/34900. I'll try to restructure these visitors a bit and send one more PR later.

When we emit E0453 (lint level attribute overruled by outer `forbid`
lint level), it could be helpful to note where the `forbid` level was
set, for the convenience of users who, e.g., believe that the correct
fix is to weaken the `forbid` to `deny`.

it's the same as linux_musl_base

The targets are:
- `arm-unknown-linux-musleabi`
- `arm-unknown-linux-musleabihf`
- `armv7-unknown-linux-musleabihf`

These mirror the existing `gnueabi` targets.

All of these targets produce fully static binaries, similar to the
x86 MUSL targets.

For now these targets can only be used with `--rustbuild` builds, as
https://github.com/rust-lang/compiler-rt/pull/22 only made the
necessary compiler-rt changes in the CMake configs, not the plain
GNU Make configs.

I've tested these targets GCC 5.3.0 compiled again musl-1.1.12
(downloaded from http://musl.codu.org/). An example `./configure`
invocation is:

```
./configure \
    --enable-rustbuild
    --target=arm-unknown-linux-musleabi \
    --musl-root="$MUSL_ROOT"
```

where `MUSL_ROOT` points to the `arm-linux-musleabi` prefix.
Usually that path will be of the form
`/foobar/arm-linux-musleabi/arm-linux-musleabi`.

Usually the cross-compile toolchain will live under
`/foobar/arm-linux-musleabi/bin`. That path should either by added
to your `PATH` variable, or you should add a section to your
`config.toml` as follows:

```
[target.arm-unknown-linux-musleabi]
cc = "/foobar/arm-linux-musleabi/bin/arm-linux-musleabi-gcc"
cxx = "/foobar/arm-linux-musleabi/bin/arm-linux-musleabi-g++"
```

As a prerequisite you'll also have to put a cross-compiled static
`libunwind.a` library in `$MUSL_ROOT/lib`. This is similar to [how
the x86_64 MUSL targets are built]
(https://doc.rust-lang.org/book/advanced-linking.html).

This is to pull in changes to support ARM MUSL targets.

This change also commits a couple of other cargo-generated changes
to other dependencies in the various Cargo.toml files.

Only export #[no_mangle] extern symbols during LTO

Fixes #34985

On Windows, ensure PATH does not contain invalid character `"`

Fixes #34959.

r? @alexcrichton

Rollup of 8 pull requests

- Successful merges: #35049, #35058, #35063, #35080, #35090, #35094, #35104, #35106
- Failed merges:

syntax_ext: format: fix ICE with bad named arguments

Fixes #35082 by guarding against a new case of malformed invocation not previously covered.

r? @alexcrichton

Rewrite `collections::LinkedList::append` doc example.

None

Revert "Remove unused methods from MultiSpan"

This reverts commit f7019a4e.

That commit removed the only way to make a suggestion with more than one substitute. That feature is not used directly by rustc but exists and is used by Clippy. Bring it back until we come up with a better solution (suggestions don't use span labels, so it would make sense for them to use their own type).
Rational there: https://github.com/Manishearth/rust-clippy/pull/1119.

r? @jonathandturner
Cc @Manishearth

intravisit: Fold functionality of IdVisitor into the regular Visitor.

Rename _ to {integer} and {float} for unknown numeric types

This PR renames _ to {integer} or {float} for unknown numeric types, to help people parse error messages that have numeric types that haven't been nailed down.

Example:
```rust
fn main() {
    let x: String = 4;
}
```

Before:
```
error[E0308]: mismatched types
 --> quicktest.rs:2:21
  |
2 |     let x: String = 4;
  |                     ^ expected struct `std::string::String`, found integral variable
  |
  = note: expected type `std::string::String`
  = note:    found type `_`

error: aborting due to previous error
```

after:
```
error[E0308]: mismatched types
 --> quicktest.rs:2:21
  |
2 |     let x: String = 4;
  |                     ^ expected struct `std::string::String`, found integral variable
  |
  = note: expected type `std::string::String`
  = note:    found type `{integer}`

error: aborting due to previous error
```
```