Remove unused LLVM related code

Ticks a few more boxes on #46437

Rollup merge of #47210 - zackmdavis:the_3rd_of_2_hardest_problems_in_computer_science, r=QuietMisdreavus

fix the doc-comment-decoration-trimming edge-case rustdoc ICE

This `horizontal_trim` function strips the leading whitespace from
doc-comments that have a left-asterisk-margin:

```
  /**
   * You know what I mean—
   *
   * comments like this!
   */
```

The index of the column of asterisks is `i`, and if trimming is deemed
possible, we slice each line from `i+1` to the end of the line. But if, in
particular, `i` was 0 _and_ there was an empty line (as in the example
given in the reporting issue), we ended up panicking trying to slice an
empty string from 0+1 (== 1).

Let's tighten our check to say that we can't trim when `i` is even the same
as the length of the line, not just when it's greater. (Any such cases
would panic trying to slice `line` from `line.len()+1`.)

Resolves #47197.

Make double ended searchers use dependent fingers

(fixes #47175)

r? @burntsushi @alexcrichton

needs uplift to beta

Add help message for incorrect pattern syntax

When I was getting started with rust I often made the mistake of using `||` instead of `|` to match multiple patterns and spent a long time staring at my code wondering what was wrong.

for example:

```
fn main() {
    let x = 1;

    match x {
        1 || 2 => println!("1 or 2"),
        _ => println!("Something else"),
    }
}

```

If you compile this with current rustc you will see

```
error: expected one of `...`, `..=`, `..`, `=>`, `if`, or `|`, found `||`
 --> test.rs:5:11
  |
5 |         1 || 2 => println!("1 or 2"),
  |          -^^ unexpected token
  |          |
  |          expected one of `...`, `..=`, `..`, `=>`, `if`, or `|` here

error: aborting due to previous error
```

With my proposed change it will show:
```
error: unexpected token `||` after pattern
 --> test.rs:5:11
  |
5 |         1 || 2 => println!("1 or 2"),
  |           ^^
  |
  = help: did you mean to use `|` to specify multiple patterns instead?

error: aborting due to previous error
```

Make normalize_and_test_predicates into a query

From #44891.

I'm not real solid on how `dep_graph` stuff works, but if a node is going to have a key (again, not sure how important that is), then the key needs to be `Copy`. So since `normalize_and_test_predicates` only had one out-of-module use, I changed that call site to use a new function, `substitute_normalize_and_test_predicates` which is the query and enables having the arguments be `Copy`. Hopefully this makes sense.

r? @nikomatsakis
and/or @michaelwoerister

Provide suggestion when trying to use method on numeric literal

New output:

```
error[E0688]: can't call method `powi` on ambiguous numeric type `{float}`
  --> $DIR/method-on-ambiguous-numeric-type.rs:12:17
   |
12 |     let x = 2.0.powi(2);
   |                 ^^^^
help: you must specify a concrete type for this numeric value, like `f32`
   |
12 |     let x = 2.0_f32.powi(2);
   |             ^^^^^^^
```

Previous output:

```
error[E0599]: no method named `powi` found for type `{float}` in the current scope
  --> src/main.rs:12:17
   |
12 |     let x = 2.0.powi(2);
   |                 ^^^^
   |
   = help: items from traits can only be used if the trait is in scope
help: the following trait is implemented but not in scope, perhaps add a `use` for it:
   |
11 | use core::num::Float;
   |
```

Fix #40985.

Try to fix a perf regression by updating log

Upgrade `log` to `0.4` in multiple crates ~and `cargo`~.
Cc: #47154.

Upgrade `log` to `0.4` in multiple crates.

rustdoc: Add missing src links for generic impls on trait pages

`implementor2item` would return `None` for generic impls so instead this clones the entire `clean::Item` into the `implementors` map which simplifies some code.

Auto merge of #47177 - michaelwoerister:erase-invalid-spans-during-metadata-encoding, r=alexcrichton

Map invalid Spans to DUMMY_SP during crate metadata encoding.

This mirrors what we do for stabilizing the incr. comp. cache and is necessary for reproducible builds. For the incr. comp. cache, we *have* to do this because the encoding there cannot represent broken Spans. Metadata encoding has to be in sync with that as not to get unexpected interactions when compiling incrementally.

This should help with fixing issue https://github.com/rust-lang/rust/issues/47066.

r? @alexcrichton

ci: use a shared script to build musl

The dist-x86_64-musl, dist-various-1 and dist-i586-gnu-i686-musl builders had different scripts to build musl. This PR creates an unified script, which makes it easier to add new musl targets and update musl and libunwind (used in the musl targets).

The libunwind is update from 3.7 to 3.9 for dist-x86_64-musl and dist-i586-gnu-i686-musl (dist-various-1 already used 3.9 version).

Refs #46437 as it also removes LLVMRustWriteDebugLocToString()

Refs #46437

The same effect can be achieved using -Cllvm-args=-debug

Refs #46437 as it removes LLVMRustSetDebug()

Support `extern` in paths

Implement the primary alternative to https://github.com/rust-lang/rust/pull/46613 + https://github.com/rust-lang/rust/pull/45771, achieving the same effect without requiring changes to other imports.
Both need to be experimentally evaluated before making further progress.

The PR also adds docs for all these related features into the unstable book.

cc https://github.com/rust-lang/rust/issues/44660
r? @nikomatsakis

Rollup of 7 pull requests

- Successful merges: #46947, #47170, #47190, #47205, #47217, #47220, #47230
- Failed merges: #47233

This `horizontal_trim` function strips the leading whitespace from
doc-comments that have a left-asterisk-margin:

  /**
   * You know what I mean—
   *
   * comments like this!
   */

The index of the column of asterisks is `i`, and if trimming is deemed
possible, we slice each line from `i+1` to the end of the line. But if, in
particular, `i` was 0 _and_ there was an empty line (as in the example
given in the reporting issue), we ended up panicking trying to slice an
empty string from 0+1 (== 1).

Let's tighten our check to say that we can't trim when `i` is even the same
as the length of the line, not just when it's greater. (Any such cases
would panic trying to slice `line` from `line.len()+1`.)

Resolves #47197.

Debuginfo Shadowed Variable test: fix check numbering

Appears to be a simple fix to restore this test. Ref issue #47163, CC @arielb1

Use name-discarding LLVM context

This is only applicable when neither of --emit=llvm-ir or --emit=llvm-bc are not
requested.

In case either of these outputs are wanted, but the benefits of such context are
desired as well, -Zfewer_names option provides the same functionality regardless
of the outputs requested.

Should be a viable fix for https://github.com/rust-lang/rust/issues/46449

Write examples for {BTree,Hash}Set::{get,replace,take}

miri: use AllocId instead of u64.

This makes @alexreg's miri allocation -> LLVM global translation more straight-forward.

r? @oli-obk

Port libpanic_abort and libpanic_unwind to CloudABI

This change ports both the libpanic* libraries to CloudABI.

The most interesting part of this pull request, however, is that it imports the CloudABI system call API into the Rust tree through a Git submodule. These will also be used by my port of libstd to CloudABI extensively, as that library obviously needs to invoke system calls to implement its primitives.

I have taken the same approach as libc: `src/libcloudabi` + `src/rustc/cloudabi_shim`. If some other naming scheme is preferred, feel free to let me know! As `libcloudabi` is pretty small, maybe it makes sense to copy, instead of using a submodule?

rustc: use {U,I}size instead of {U,I}s shorthands.

`Us`/`Is` come from a time when `us` and `is` were the literal suffixes that are now `usize` / `isize`.

r? @nikomatsakis

doc: improve None condition doc for `checked_div` and `checked_rem`

This commit improves the condition mentioned in the docs for which `checked_div` and `checked_rem` return `None`.

For signed division, the commit changes "the operation results in overflow" to "the division results in overflow", otherwise there is room for misinterpretation for `checked_rem`: Without considering overflow, `MIN % -1` would be simply zero, allowing the misinterpretation that "the operation" does not result in overflow in this case. This ambiguity is removed using "when the division results in overflow".

For unsigned division, the condition for `None` should be simply when `rhs == 0`, as no other overflow is possible.

Bump to 1.25.0

* Bump the release version to 1.25
* Bump the bootstrap compiler to the recent beta
* Allow using unstable rustdoc features on beta - this fix has been applied to
  the beta branch but needed to go to the master branch as well.

Add 'Span::parent()' and 'Span::source()' to proc_macro API.

As the title suggests: a couple of useful methods for `proc_macro`.

Issue 46976

ICE is due to an empty path segments, so I set the path to be the same as the in band ty params symbol. (I think this is how regular generics end up being handled?)

Pinging @cramertj, this is your code I'm editing here.

Restore working debuginfo tests by trimming comments from non-header directive lines

I noticed when adding a debuginfo test that nothing I did caused the test to fail. Tracing back this seems to have been caused by 3e6c83de which broke parsing of the command/check lines, leaving all tests passing without any checking. This commit provides a basic (although still not very robust) restoration of tests and a should-fail test which checks the parser is running

Rollup of 5 pull requests

- Successful merges: #46987, #47165, #47173, #47202, #47216
- Failed merges: