rustc_trans: keep LLVM types for trait objects anonymous.

Fixes #47638 by reverting the addition of readable LLVM trait object type names.
r? @nikomatsakis

[MSP430] Don't enable trap_unreachable option by default on msp.

Since MSP430 doesn't meaningfully support faulting on illegal
instructions, LLVM generates a call to abort() function instead
of a trap instruction. Such calls are 4 bytes long, and that is
too much overhead for such small target.

r? @alexcrichton

rustc: Add an option to default hidden visibility

This commit adds a new option to target specifictions to specify that symbols
should be "hidden" visibility by default in LLVM. While there are no existing
targets that take advantage of this the `wasm32-unknown-unknown` target will
soon start to use this visibility. The LLD linker currently interprets `hidden`
as "don't export this from the wasm module" which is what we want for 90% of our
functions. While the LLD linker does have a "export this symbol" argument which
is what we use for other linkers, it was also somewhat easier to do this change
instead which'll involve less arguments flying around. Additionally there's no
need for non-`hidden` visibility for most of our symbols!

This change should not immediately impact the wasm targets as-is, but rather
this is laying the foundations for soon integrating LLD as a linker for wasm
code.

rustc: Add some defines for LLVM 7 compat

I was testing out the tip support to see what's going on with wasm, and this was
I believe the only issue encountered with LLVM 7 support so far.

Ignore run-pass/sse2 when using system LLVM

This is a test of `target_feature`, which needs a rust-specific patch to
LLVM to add `MCSubtargetInfo::getFeatureTable()`.

Update associated constants error message

Fixes #47570.

rustc_trans: clobber $1 (aka $at) on mips

This copies what clang does. There is a long explanation as to why this is needed in the clang source (tools/clang/lib/Basic/Targets/Mips.h).

std: use more portable error number in from_raw_os_error docs

On MIPS, error number 98 is not `EADDRINUSE` (it is `EPROTOTYPE`). To fix the resulting test failure this causes, use a more portable error number in the example documentation. `EINVAL` shold be more reliable because it was defined in the original Unix as 22 so hopefully most derivatives have defined it the same way.

Fix regression: account for trait methods in arg count mismatch error

Fixed #47706 (https://github.com/rust-lang/rust/issues/47706#issuecomment-361161495)

Original PR #47747 missed methods on trait definitions.

This edit was done in GitHub. I think I got the signature of the variant right, going by the ICE debug output and the other cases above.

Marked Debug implementations for primitive types as #[inline]

Change for issue #47792.

use correct casing for rename suggestions

If the original name is uppercase, use camel case. Otherwise, use snake
case.

Move Duration to libcore

Fixes #46520; should be merged after #46508.

Since MSP430 doesn't meaningfully support faulting on illegal
instructions, LLVM generates a call to abort() function instead
of a trap instruction. Such calls are 4 bytes long, and that is
too much overhead for such small target.

This commit adds a new option to target specifictions to specify that symbols
should be "hidden" visibility by default in LLVM. While there are no existing
targets that take advantage of this the `wasm32-unknown-unknown` target will
soon start to use this visibility. The LLD linker currently interprets `hidden`
as "don't export this from the wasm module" which is what we want for 90% of our
functions. While the LLD linker does have a "export this symbol" argument which
is what we use for other linkers, it was also somewhat easier to do this change
instead which'll involve less arguments flying around. Additionally there's no
need for non-`hidden` visibility for most of our symbols!

This change should not immediately impact the wasm targets as-is, but rather
this is laying the foundations for soon integrating LLD as a linker for wasm
code.

I was testing out the tip support to see what's going on with wasm, and this was
I believe the only issue encountered with LLVM 7 support so far.

This is a test of `target_feature`, which needs a rust-specific patch to
LLVM to add `MCSubtargetInfo::getFeatureTable()`.

This copies what clang does. There is a long explanation as to why this
is needed in the clang source (tools/clang/lib/Basic/Targets/Mips.h).

On MIPS, error number 98 is not EADDRINUSE (it is EPROTOTYPE). To fix the
resulting test failure this causes, use a more portable error number in
the example documentation. EINVAL shold be more reliable because it was
defined in the original Unix as 22 so hopefully most derivatives have
defined it the same way.

Rollup of 12 pull requests

- Successful merges: #47515, #47603, #47718, #47732, #47760, #47780, #47822, #47826, #47836, #47839, #47853, #47855
- Failed merges:

rustdoc: Fix link title rendering with hoedown

The link title needs to be HTML escaped.

It was broken by #47046.

r? @QuietMisdreavus

Increase test coverage of use_nested_groups

r? @nikomatsakis

Document that `Index` ops can panic on `HashMap` & `BTreeMap`.

Fixes https://github.com/rust-lang/rust/issues/47011.

Add per-stage RUSTFLAGS: RUSTFLAGS_STAGE_{0,1,2} and RUSTFLAGS_STAGE_NOT_0

Fixes #47658.

r? @alexcrichton

Whitelist v7 feature for ARM and AARCH64.

Needed for `v7` features in `coresimd`.

See https://github.com/rust-lang-nursery/stdsimd/blob/b2f7be24d5043a88427f9a5258ca9a51ede6d029/coresimd/src/arm/v7.rs#L40 which used to work but doesn't anymore.

r? alexcrichton

Whitelist aes x86 feature flag

Required to fix https://github.com/rust-lang-nursery/stdsimd/issues/295 in stdsimd.

Closes #44544 .

r? @alexcrichton

Add line numbers and columns to error messages spanning multiple files

If an error message is emitted that spans several files, only the
primary file currently has line and column data attached. This is
useful information, even in files other than the one in which the error
occurs. We can often work out which line and column the error
corresponds to in other files — in this case it is helpful to add them
(in the case of ambiguity, the first relevant line/column is picked,
which is still helpful than none).

implement Send for process::Command on unix

closes https://github.com/rust-lang/rust/issues/47751

Run rustfmt and add doc comments to libsyntax/ext/tt/macro_parser.rs

Similar to #47603

cc @theotherphil since you reviewed my other PR 😄

And because they are already assigned on #47603:

r? @arielb1

Make run-pass/env-home-dir.rs test more robust

Remove the assumption that home_dir always returns Some.

This allows the test to be executed with [cross](https://github.com/japaric/cross).

Run rustfmt and add doc comments to libsyntax/ext/tt/quoted.rs

I was already going to try to understand this code to try to implement rust-lang/rfcs#2298. I figured I would put that knowledge into comments and share... This PR contains _no changes_ to the code itself -- just formatting and comments.

I'm not sure what the best way to do this is. I plan to make more such PR for other files, but I figured it would have fewer conflicts if I do it file by file...

Punctuation and clarity fixes.

syntax: Lower priority of `+` in `impl Trait`/`dyn Trait`

Now you have to write `Fn() -> (impl A + B)` instead of `Fn() -> impl A + B`, this is consistent with priority of `+` in trait objects (`Fn() -> A + B` means `(Fn() -> A) + B`).

To make this viable I changed the syntax to also permit `+` in return types in function declarations
```
fn f() -> dyn A + B { ... } // OK, don't have to write `-> (dyn A + B)`

// This is acceptable, because `dyn A + B` here is an isolated type and
// not part of a larger type with various operator priorities in play
// like `dyn A + B` in `Fn() -> dyn A + B` despite syntax similarities.
```
but you still have to use `-> (dyn A + B)` in function types and function-like trait object types (see this PR's tests for examples).

This can be a breaking change for code using `impl Trait` on nightly. The thing that is most likely to break is `&impl A + B`, it needs to be rewritten as `&(impl A + B)`.

cc https://github.com/rust-lang/rust/issues/34511 https://github.com/rust-lang/rust/issues/44662 https://github.com/rust-lang/rfcs/pull/438

Replace "lvalue" terminology with "place".

See #46425 for the previous PR (which only changed MIR-related code).

r? @nikomatsakis