in librustc in several places

To avoid potential duplicate diagnostics and separate the error reporting logic

This reverts commit d97379a.

Format libcore with rustfmt (including tests and benches)

Important: two small non-rustfmt changes that will need close review:

- I added `#[rustfmt::skip]` to two manually arranged tables in src/libcore/benches/ascii.rs; see first commit in the PR.
- I added `// ignore-tidy-filelength` to src/libcore/ptr/mod.rs because rustfmt puts it over tidy's 3000 line limit; see second commit in the PR. I filed rust-lang#66891 to follow up on breaking up that file. For now though having it be formatted is more important than having it below the line limit.

---

As with my previous formatting PRs, I am avoiding causing merge conflicts in other PRs by only touches those files that are not involved in any currently open PR. Files that appear in new PRs between when this PR is opened and when it makes it to the top of the bors queue will be reverted from this PR.

The list of files involved in open PRs is determined by querying GitHub's GraphQL API [with this script](https://gist.github.com/dtolnay/aa9c34993dc051a4f344d1b10e4487e8).

With the list of files from the script in outstanding_files, the relevant commands were:

```
$ find src/libcore -name '*.rs' \
    | xargs rustfmt --edition=2018 --unstable-features --skip-children
$ rg libcore outstanding_files | xargs git checkout --
```

To confirm no funny business:

```
$ git checkout $THIS_COMMIT^
$ git show --pretty= --name-only $THIS_COMMIT \
    | xargs rustfmt --edition=2018 --unstable-features --skip-children
$ git diff $THIS_COMMIT  # there should be no difference
```

r? @Dylan-DPC

resolve: Resolve visibilities on fields with non-builtin attributes

Follow-up to rust-lang#66669.

The first commit is primary (and also a backport candidate), the other ones are further cleanups.
In this case it's not strictly necessary to avoid reporting errors during speculative resolution because 1) all visibilities are resolved non-speculatively sooner or later and 2) error reporting infrastructure merges identical errors with identical spans anyway.

Fixes rust-lang#67006
r? @matthewjasper

…dtwco

Print the visibility in `print_variant`.

r? @davidtwco
cc @dtolnay for `syn` awareness.

… r=davidtwco

Simplify `check_decl_no_pat`.

r? @davidtwco

…ichton

libstd miri tests: avoid warnings

Ignore tests in a way that all the code still gets compiled, to get rid of all the "unused" warnings that otherwise show up when running the test suite in Miri.

Added ExactSizeIterator bound to return types

Fixes rust-lang#66865

…, r=Amanieu

Simplify `Layout::extend_packed`

fix miri step debug printing

r? @oli-obk

Do not ICE rust-lang#67123

Fixes rust-lang#67123

r? @matthewjasper

…ference, r=cramertj

Move `Layout`s instead of binding by reference

inline some common methods on OsStr

Closes rust-lang#67150