Show clearer error message when #![deny(warnings)] escalates a warning

Addresses #30730

Make errors for unnecessary visibility qualifiers consistent

This PR refactors away `syntax::parse::parser::ParsePub` so that unnecessary visibility qualifiers on variant fields are reported not by the parser but by `privacy::SanePrivacyVisitor` (thanks to @petrochenkov's drive-by improvements in #31919).

r? @nikomatsakis

tests: add test for empty <>

Rust allows to specify an empty list of type and lifetime parameters, but there are no tests for it:

```
user@UNIT-326 [12:53:45] [~/projects/rust] [diamonds-and-rust]
-> % grep "<>" -R src/test
src/test/compile-fail/generic-type-params-name-repr.rs:    // And don't print <> at all when there's just defaults.
src/test/debuginfo/issue22656.rs:// when trying to handle a Vec<> or anything else that contains zero-sized
```

So let's add them! Besides it's such a wonderful opportunity to put a reference to Judas Priest band into the branch name ;)

Exclude 0.0.0.0 from the list of globally routable addresses

Rollup of 7 pull requests

- Successful merges: #31772, #32083, #32084, #32092, #32099, #32103, #32115
- Failed merges:

Update a spelling inconsistency

L26: "zero cost" -> "zero-cost"

Fixed link in ownership documentation

Changed "[vector]" to a link to the vector documentation.

Clarify documentation for string slicing (Index impls)

Clarify documentation for string slicing (Index impls)

- Mention the sugared syntax for the implementations, since it's not
  apparent from the docs that `Index<Range<usize>>` corresponds to
  `&self[a..b]`.
- Be specific in that start <= end and end <= len

This is just one fix in response to #32057

Update syntax index with OpAssign traits

book: Update syntax index with OpAssign traits

The traits are stable from Rust 1.8.

Fix typos - mismatching parentheses in comments

Fixes mismatching parentheses in the comments of precision example.

r? @steveklabnik

reference.md: clarify the limitation of type alias on an enum

Tentatively define the current behavior as the specification.

Cf. rust-lang/rust#26264, rust-lang/rust#28556, rust-lang/rust#30936

Clarify the semantics of enum discriminants

cf. https://doc.rust-lang.org/error-index.html#E0082

> The default type for enum discriminants is isize, but it can be adjusted by adding the repr attribute to the enum declaration.

It would be great if anyone could check my English.

mk: Distribute fewer TARGET_CRATES

Right now everything in TARGET_CRATES is built by default for all non-fulldeps
tests and is distributed by default for all target standard library packages.
Currenly this includes a number of unstable crates which are rarely used such as
`graphviz` and `rbml`>

This commit trims down the set of `TARGET_CRATES`, moves a number of tests to
`*-fulldeps` as a result, and trims down the dependencies of libtest so we can
distribute fewer crates in the `rust-std` packages.

rustbuild: Fix building from an empty directory

A stray shutil.rmtree happened when it shouldn't have happened, causing the
entire build to fail.

Add error file for E0152

It completes #31818.

However it is not complete yet:
 * test will need to be updated
 * the file name displayed is a bit too unclear.

I'm not sure yet what's the "correct" file name to display. If anyone has an idea on this, it'd be very appreciated.

r? @brson

implement the `?` operator

The `?` postfix operator is sugar equivalent to the try! macro, but is more amenable to chaining:
`File::open("foo")?.metadata()?.is_dir()`.

`?` is accepted on any *expression* that can return a `Result`, e.g. `x()?`, `y!()?`, `{z}?`,
`(w)?`, etc. And binds more tightly than unary operators, e.g. `!x?` is parsed as `!(x?)`.

cc #31436

---

cc @aturon @EddyB

Rename ClosureKind variants and stop re-exporting them.

L26: "zero cost" -> "zero-cost"

libsyntax: be more accepting of whitespace in lexer

Fixes #29590.

Perhaps this may need more thorough testing?

r? @Aatch

Fix building libstd on emscripten targets.

The main cause of the problem is that libstd/os/mod.rs treats emscripten targets as an alias of linux targets, whereas liblibc treats emscripten targets as musl-compliant, so it gets a slightly different struct stat64 defined.
This commit adds conditional compilation checks to use the correct timestamp format on fs metadata functions in the case of compiling to emscripten targets.

This commit also depends needs https://github.com/ashleysommer/rust/commit/f1575cff2d631e977038fdba3fa3422ba5f8f2fe applied in order to successfully build libstd with emscripten target.

Cf. rust-lang/rust#26264
Signed-off-by: NNODA, Kai <nodakai@gmail.com>

Right now everything in TARGET_CRATES is built by default for all non-fulldeps
tests and is distributed by default for all target standard library packages.
Currenly this includes a number of unstable crates which are rarely used such as
`graphviz` and `rbml`>

This commit trims down the set of `TARGET_CRATES`, moves a number of tests to
`*-fulldeps` as a result, and trims down the dependencies of libtest so we can
distribute fewer crates in the `rust-std` packages.

- Mention the sugared syntax for the implementations, since it's not
  apparent from the docs that `Index<Range<usize>>` corresponds to
  `&self[a..b]`.
- Be specific in that start <= end and end <= len

The `?` postfix operator is sugar equivalent to the try! macro, but is more amenable to chaining:
`File::open("foo")?.metadata()?.is_dir()`.

`?` is accepted on any *expression* that can return a `Result`, e.g. `x()?`, `y!()?`, `{z}?`,
`(w)?`, etc. And binds more tightly than unary operators, e.g. `!x?` is parsed as `!(x?)`.

cc #31436

Changed "[vector]" to a link to the vector documentation.

- make sure we copy the third party objects (crt*.o) to the target stage directory.
- apply the x86_64-musl logic also to the i686-musl target.

---

r? @alexcrichton

It would be great if someone could check my English.

Squashed 10 commits:
1) The main cause of the problem is that libstd/os/mod.rs treats emscripten targets as an alias of linux targets, whereas liblibc treats emscripten targets as musl-compliant, so it gets a slightly different struct stat64 defined.
This commit adds conditional compilation checks to use the correct timestamp format on fs metadata functions in the case of compiling to emscripten targets.

2) Update previous commit to comply with rust formatting standards.
Removed tab characters, remove trailing whitespaces.

3) Move emscripten changes into their own file under libstd/os/emscripten
Put libstd/os/linux/fs back to the way it was.

4) Cannot use stat.st_ctim on emscripten to get created time.

5) Remove compile-time conditionals for target_env = musl, it looks like musl builds compile fine already.

6) Undone some formatting changes that are no longer needed,
Removed some more target_env="musl" compilation checks that I missed from my previous commit.

7) upgrade to liblibc e19309c, it fixes the differences in the musl stat and stat64 definitions.

8) Undo the compile-time checks to check for emscripten (or musl targets) in the FileAttr struct.
No longer needed after updating liblibc to e19309c.

9) Change the MetadataExt implementation of emscripten fs.rs module to match the changes in new liblibc.

10) remove a stray return statement, should have been removed in the previous commit.

Fixes #9447

This adds support for fused multiply-add and multiply-subtract vector intrinsics for 128 and 256-bit vectors of `f32` and `f64`. These correspond to the intrinsics [listed here](https://software.intel.com/en-us/node/523929) except for the `_ss` and `_sd` variants. The intrinsics added are:

 * `fmadd`
 * `fmaddsub`
 * `fmsub`
 * `fmsubadd`
 * `fnmadd`
 * `fnmsub`

The “fma” target feature must be enabled by passing `-C target-feature=+fma` to rustc when using these, otherwise LLVM will complain.

I verified locally that the `x86_mm256_fmadd_ps` and `x86_mm256_fmsub_ps` work.

Fix panic on string slicing error to truncate the string

The string may be arbitrarily long, but we want to limit the panic
message to a reasonable length. Truncate the string if it is too long
(simply to char boundary).

Also add details to the start <= end message. I think it's ok to flesh
out the code here, since it's in a cold function.

Fixes #32063

Adding -Wno-error is more reliable and simple than trying to modify existing
flags. We've been using this in Debian already for the past few releases.
Making this change also encourages future maintainers towards "best practises".
Also take the opportunity to use the same method at all places in the file.

Using spaces in the install path causes the issue in #31293.

Signed-off-by: NNODA, Kai <nodakai@gmail.com>