We want the lifetimes of the patterns contained in the matrix and the
candidate `PatStack` to be the same so that they can be mixed together.
A lot of this would not be necessary if `SmallVec` was covariant in its
type argument (see https://github.com/servo/rust-smallvec/issues/146).

The exact same logic was used in check_arms and check_match to build the
matrix of relevant patterns. It would actually probably have been a bug
if it was not the case, since exhaustiveness checking should be the same
as checking reachability of an additional `_ => ...` match branch.

Miri engine: proper support for `Assert` MIR terminators

This puts down the basis for https://github.com/rust-lang/miri/issues/1070, and I also did some clean-up. The Miri side of this is at https://github.com/rust-lang/miri/pull/1084.

r? @oli-obk

Rollup of 5 pull requests

Successful merges:

 - #66245 (Conditional compilation for sanitizers)
 - #66654 (Handle const-checks for `&mut` outside of `HasMutInterior`)
 - #66822 (libunwind_panic: adjust miri panic hack)
 - #66827 (handle diverging functions forwarding their return place)
 - #66834 (rustbuild fixes)

Failed merges:

r? @ghost

rustbuild fixes

When upgrading Debian's rustc to 1.38 I needed these patches:

(1) In order to cross-compile rustc 1.38 and take it through the full rustbuild process including install, I needed the first patch.

(2) In order to build rustc 1.38 using rustc 1.38 itself I need to set --cap-lints warn, otherwise I get this error:

~~~~
error: unnecessary `unsafe` block
   --> src/bootstrap/builder.rs:148:19
    |
148 |             name: unsafe { ::std::intrinsics::type_name::<S>() },
    |                   ^^^^^^ unnecessary `unsafe` block
    |
note: lint level defined here
   --> src/bootstrap/lib.rs:107:9
    |
107 | #![deny(warnings, rust_2018_idioms, unused_lifetimes)]
    |         ^^^^^^^^
    = note: `#[deny(unused_unsafe)]` implied by `#[deny(warnings)]`

error: aborting due to previous error

error: could not compile `bootstrap`.

~~~~

In order to set --cap-lints warn however, I need bootstrap.py not to clobber RUSTFLAGS. (This worked previously, not sure if it was broken intentionally but we would like support for it.)

handle diverging functions forwarding their return place

Fixes https://github.com/rust-lang/miri/issues/1075: the shim around diverging closures turned into function pointers actually "obtains" a return place inside a diverging function, but just uses it as the return place for a diverging callee. Handle this by using NULL places.

This is kind of a hack as it breaks our invariant that all places are dereferencable, but we'd eventually let raw pointers break that anyway I assume so that seems fine.

r? @oli-obk

libunwind_panic: adjust miri panic hack

We adjust the Miri hack in libpanic_unwind such that even with `cfg(miri)`, we build a version of libpanic_unwind that actually works.

This is needed to resolve https://github.com/integer32llc/rust-playground/issues/548.

r? @oli-obk @alexcrichton

Handle const-checks for `&mut` outside of `HasMutInterior`

Addresses [this comment](https://github.com/rust-lang/rust/pull/64470#discussion_r328200508).

Const-checking relied on `HasMutInterior` to forbid `&mut` in a const context. This was strange because all we needed to do was look for an `Rvalue::Ref` with a certain `BorrowKind`, whereas the `Qualif` traits are specifically meant to get the qualifs for a *value*. This PR removes that logic from `HasMutInterior` and moves it into `check_consts::Validator`.

As a result, we can now properly handle qualifications for `static`s, which had to be ignored previously since you can e.g. borrow a static `Cell` from another `static`. We also remove the `derived_from_illegal_borrow` logic, since it is no longer necessary; we give good errors for subsequent reborrows/borrows of illegal borrows.

Conditional compilation for sanitizers

Configure sanitize option when compiling with a sanitizer to make
it possible to execute different code depending on whether given
sanitizer is enabled or not.

Rollup of 7 pull requests

Successful merges:

 - #66346 (Replace .unwrap() with ? in std::os::unix::net)
 - #66789 (rustc: move mir::SourceScopeLocalData to a field of SourceScopeData.)
 - #66850 (rustc: hide HirId's fmt::Debug output from -Z span_free_formats.)
 - #66905 (rustc_plugin: Remove some remaining plugin features)
 - #66907 (rustc: don't just show raw DefIndex's in BrNamed's fmt::Debug impl.)
 - #66918 (Add crc and crypto to target feature whitelist on arm)
 - #66926 (add reusable MachineStop variant to Miri engine error enum)

Failed merges:

r? @ghost

add reusable MachineStop variant to Miri engine error enum

Replace the Miri-tool-specific `Exit` error variant with something dynamically typed that all clients of the Miri engine can use.

r? @oli-obk
Cc https://github.com/rust-lang/rust/issues/66902

Add crc and crypto to target feature whitelist on arm

aarch32 (ARMv8 32-bit) supports crc and crypto.

rustc: don't just show raw DefIndex's in BrNamed's fmt::Debug impl.

Context: these `fmt::Debug` impls only get used with `-Z verbose` (which some tests use).

I was going to print the path like in #66850 (or rather, use `DefId`'s `fmt::Debug`, which is close but not as nice), but then I realized that most of the `DefId`s were `crate0:DefIndex(0)`, i.e. the crate root.
As the crate root is not a lifetime, they're clearly dummies of some sort, and we don't have to print anything other than the name for them.

This means that out of all the tests, there's only 5 instances of `BrNamed` that now print the full path to the lifetime parameter, and everything else is shorter instead, which doesn't feel too bad.

cc @nikomatsakis

rustc_plugin: Remove some remaining plugin features

- Plugin arguments (`#![plugin(my_plugin(args))]`) are no longer supported.
- Registering additional plugins from command line (`-Z extra-plugins=my_plugin`) is no longer supported, `-Z crate-attr=plugin(my_plugin)` can be used instead.
- Lint `plugin_as_library` is removed as mostly useless now, when plugins exist as a compatibility feature with greatly reduced functionality.
- Plugins registering additional LLVM passes (`Registry::register_llvm_pass`) are no longer supported, `-C                   passes=my_passes` can be used instead.

r? @Centril

rustc: hide HirId's fmt::Debug output from -Z span_free_formats.

This replaces the only occurrences of `HirId {...}` from tests with paths, i.e.:
```rust
[closure@HirId { owner: DefIndex(4), local_id: 15 } q:&i32, t:&T]
```
becomes, after this PR:
```rust
[closure@foo<T>::{{closure}}#0 q:&i32, t:&T]
```

r? @oli-obk cc @michaelwoerister

rustc: move mir::SourceScopeLocalData to a field of SourceScopeData.

By having one `ClearCrossCrate<SourceScopeLocalData>` for each scope, as opposed to a single `ClearCrossCrate` for all the `SourceScopeLocalData`s, we can represent the fact that some scopes have `SourceScopeLocalData` associated with them, and some don't.

This is useful when doing MIR inlining across crates, because the `ClearCrossCrate` will be `Clear` for the cross-crate MIR scopes and `Set` for the local ones.

Also see https://github.com/rust-lang/rust/pull/66203#issuecomment-555589574 for some context around this approach.

Fixes #51314.

Replace .unwrap() with ? in std::os::unix::net

As people like to copy examples, this gives them good habits.

Remove a useless test

Configure sanitize option when compiling with a sanitizer to make
it possible to execute different code depending on whether given
sanitizer is enabled or not.

Rollup of 9 pull requests

Successful merges:

 - #66503 (More useful test error messages on should_panic(expected=...) mismatch)
 - #66662 (Miri: run panic-catching tests in liballoc)
 - #66679 (Improve lifetime errors with implicit trait object lifetimes)
 - #66726 (Use recursion_limit for const eval stack limit)
 - #66790 (Do `min_const_fn` checks for `SetDiscriminant`s target)
 - #66832 (const_prop: detect and avoid catching Miri errors that require allocation)
 - #66880 (Add long error code explanation message for E0203)
 - #66890 (Format liballoc with rustfmt)
 - #66896 (pass Queries to compiler callbacks)

Failed merges:

r? @ghost

pass Queries to compiler callbacks

https://github.com/rust-lang/rust/pull/66791 made it impossible to access the tcx in the callbacks; this should fix that.

r? @Zoxc

Format liballoc with rustfmt

Same strategy as #66691 -- 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/liballoc -name '*.rs' \
    | xargs rustfmt --edition=2018 --unstable-features --skip-children
$ rg liballoc 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

Add long error code explanation message for E0203

Addressed some of #61137

r? @GuillaumeGomez

const_prop: detect and avoid catching Miri errors that require allocation

r? @wesleywiser @oli-obk