ci: run mir-opt tests on PR CI also as 32-bit (for `EMIT_MIR_FOR_EACH_BIT_WIDTH`).

Background: #69916 and [`src/test/mir-opt/README.md`](https://github.com/rust-lang/rust/blob/master/src/test/mir-opt/README.md):
> By default 32 bit and 64 bit targets use the same dump files, which can be problematic in the
presence of pointers in constants or other bit width dependent things. In that case you can add
>
> ```
> // EMIT_MIR_FOR_EACH_BIT_WIDTH
> ```
>
> to your test, causing separate files to be generated for 32bit and 64bit systems.

However, if you change the output of such a test (intentionally or not), or if you add a test and it varies between 32-bit and 64-bit platforms, you have to run this command (for a x64 linux host):
`./x.py test --stage 1 --target x86_64-unknown-linux-gnu --target i686-unknown-linux-gnu --bless  src/test/mir-opt`

Otherwise, bors trying to merge the PR will fail, since we test 32-bit targets there.
But we don't on PR CI, which means there's no way the PR author would know (unless they were burnt by this already and know what to look for).

This PR resolves that by running `mir-opt` tests for ~~`i686-unknown-linux-gnu`~~, on PR CI.
**EDIT**: switched to `armv5te-unknown-linux-gnueabi` to work around LLVM 7 crashes (see https://github.com/rust-lang/compiler-builtins/pull/311#issuecomment-612270089), found during testing.

cc @rust-lang/wg-mir-opt @rust-lang/infra

Take `impl Into<DefId>` for query methods on `TyCtxt`

Alternative implementation of #70956. cc #70853.

Make LLVM version suffix independent of rustc version on dev channel

Remove rustc version from LLVM version suffix on dev channel,
avoiding the need for full rebuilds when switching between
branches with different LLVM submodule & rustc version.

Note: To avoid full rebuild, on subsequent LLVM submodule update, copy the
current value of `LLVM_VERSION_SUFFIX` from `build/*/llvm/build/CMakeCache.txt`,
to `version-suffix` in `config.toml`.

submodules: update clippy from d342cee7 to af5940b7

Changes:
````
Allow UUID style formatting for `inconsistent_digit_grouping` lint
rustup https://github.com/rust-lang/rust/pull/70986
rustup https://github.com/rust-lang/rust/pull/69745
Rustup to https://github.com/rust-lang/rust/pull/70913
compare with the second largest instead of the smallest variant
Revert "Downgrade new_ret_no_self to pedantic"
Check for clone-on-copy in argument positions
Check fn header along with decl when suggesting to implement trait
Downgrade implicit_hasher to pedantic
Move cognitive_complexity to nursery
Run fmt and update test
Use int assoc consts in MANUAL_SATURATING_ARITHMETIC
Use int assoc consts in checked_conversions lint
Use primitive type assoc consts in more tests
Use integer assoc consts in more lint example code
Don't import primitive type modules
Use assoc const NAN for zero_div_zero lint
Fix float cmp to use assoc fxx::EPSILON
Fix NAN comparison lint to use assoc NAN
Refine lint message.
Lint on opt.as_ref().map(|x| &**x).
Include OpAssign in suspicious_op_assign_impl
result_map_or_into_option: fix syntax error in example
result_map_or_into: fix dogfood_clippy error => {h,l}int
CONTRIBUTING.md: fix broken triage link
result_map_or_into_option: fix `cargo dev fmt --check` errors
result_map_or_into_option: move arg checks into tuple assignment
result_map_or_into_option: add `opt.map_or(None, |_| Some(y))` test
result_map_or_into_option: destructure lint tuple or return early
result_map_or_into_option: add good and bad examples
result_map_or_into_option: explicitly note absence of known problems
Downgrade new_ret_no_self to pedantic
Downgrade unreadable_literal to pedantic
Update CONTRIBUTING.md
Rename rustc -> rustc_middle in doc links
result_map_or_into_option: add lint to catch manually adpating Result -> Option
Move matches test in matches module
Run update_lints
Make lint modules private
Don't filter lints in code generation functions
Build lint lists once and the reuse them to update files
Get rid of Lint::is_internal method
Clean up update_lints
Downgrade inefficient_to_string to pedantic
Downgrade trivially_copy_pass_by_ref to pedantic
Downgrade let_unit_value to pedantic
````
Fixes #70993

r? @Dylan-DPC

[windows] Add testscase for self-contained executables and fix pthread linking

Fixes https://github.com/rust-lang/rust/issues/71061

Rollup of 4 pull requests

Successful merges:

 - #67766 (Fix warning for unused variables in or pattern (issue #67691))
 - #71013 (Pass the `PlaceElem::Index` local to `visit_local`)
 - #71064 (fix issue 69130)
 - #71069 (Remove some usage of `DUMMY_HIR_ID`)

Failed merges:

r? @ghost

Remove some usage of `DUMMY_HIR_ID`

Use `ObligationClause::dummy()` when appropriate or replace `hir::DUMMY_HIR_ID`by `hir::CRATE_HIR_ID`, as used in `ObligationClause::dummy()`.

fix issue 69130

Closes #69130.

Pass the `PlaceElem::Index` local to `visit_local`

Fixes https://github.com/rust-lang/rust/issues/71008

cc @rust-lang/wg-mir-opt

r? @spastorino

Fix warning for unused variables in or pattern (issue #67691)

Is this a good way to fix it?

Also, the tests fail, the "fixed" code output says `{ i, j }` instead of `{ i, j: _ }`, how can I fix that?

Use `ObligationClause::dummy()` when appropriate or replace
`hir::DUMMY_HIR_ID` by `hir::CRATE_HIR_ID`, as used in
`ObligationClause::dummy()`.

Rollup of 6 pull requests

Successful merges:

 - #71029 (Partial work on building with Cargo)
 - #71034 (Clean up E0515 explanation)
 - #71041 (Update links of `rustc guide`)
 - #71048 (Normalize source when loading external foreign source into SourceMap)
 - #71053 (Add some basic docs to `sym` and `kw` modules)
 - #71057 (Clean up E0516 explanation)

Failed merges:

r? @ghost

Clean up E0516 explanation

r? @Dylan-DPC

Add some basic docs to `sym` and `kw` modules

I was looking into improving some Clippy documentation but was missing a
place that explains the `kw` and `sym` modules from rustc.

This adds some very basic usage documentation to these modules.

Normalize source when loading external foreign source into SourceMap

The compiler normalizes source when reading files initially (removes BOMs, etc), but not when loading external sources.

This leads to the external source matching according to the `src_hash`, but differing internally because it was not normalized.

Fixes #70874.

Update links of `rustc guide`

Picks up the things we left behind in the transition, hopefully they're last ones.

r? @spastorino

Clean up E0515 explanation

r? @Dylan-DPC

Partial work on building with Cargo

This cherry picks the commits I'm directly approving from #70999, I want to land them so that that PR is smaller.

Update rustc-dev-guide

This should finally fix toolstate

r? @JohnTitor

Changes:
````
Allow UUID style formatting for `inconsistent_digit_grouping` lint
rustup https://github.com/rust-lang/rust/pull/70986
rustup https://github.com/rust-lang/rust/pull/69745
Rustup to https://github.com/rust-lang/rust/pull/70913
compare with the second largest instead of the smallest variant
Revert "Downgrade new_ret_no_self to pedantic"
Check for clone-on-copy in argument positions
Check fn header along with decl when suggesting to implement trait
Downgrade implicit_hasher to pedantic
Move cognitive_complexity to nursery
Run fmt and update test
Use int assoc consts in MANUAL_SATURATING_ARITHMETIC
Use int assoc consts in checked_conversions lint
Use primitive type assoc consts in more tests
Use integer assoc consts in more lint example code
Don't import primitive type modules
Use assoc const NAN for zero_div_zero lint
Fix float cmp to use assoc fxx::EPSILON
Fix NAN comparison lint to use assoc NAN
Refine lint message.
Lint on opt.as_ref().map(|x| &**x).
Include OpAssign in suspicious_op_assign_impl
result_map_or_into_option: fix syntax error in example
result_map_or_into: fix dogfood_clippy error => {h,l}int
CONTRIBUTING.md: fix broken triage link
result_map_or_into_option: fix `cargo dev fmt --check` errors
result_map_or_into_option: move arg checks into tuple assignment
result_map_or_into_option: add `opt.map_or(None, |_| Some(y))` test
result_map_or_into_option: destructure lint tuple or return early
result_map_or_into_option: add good and bad examples
result_map_or_into_option: explicitly note absence of known problems
Downgrade new_ret_no_self to pedantic
Downgrade unreadable_literal to pedantic
Update CONTRIBUTING.md
Rename rustc -> rustc_middle in doc links
result_map_or_into_option: add lint to catch manually adpating Result -> Option
Move matches test in matches module
Run update_lints
Make lint modules private
Don't filter lints in code generation functions
Build lint lists once and the reuse them to update files
Get rid of Lint::is_internal method
Clean up update_lints
Downgrade inefficient_to_string to pedantic
Downgrade trivially_copy_pass_by_ref to pedantic
Downgrade let_unit_value to pedantic
````
Fixes #70993

I was looking into improving some Clippy documentation but was missing a
place that explains the `kw` and `sym` modules from rustc.

Handle `impl Trait` where `Trait` has an assoc type with missing bounds

When encountering a type parameter that needs more bounds the trivial case is `T` `where T: Bound`, but it can also be an `impl Trait` param that needs to be decomposed to a type param for cleaner code. For example, given

```rust
fn foo(constraints: impl Iterator) {
    for constraint in constraints {
        println!("{:?}", constraint);
    }
}
```

the previous output was

```
error[E0277]: `<impl Iterator as std::iter::Iterator>::Item` doesn't implement `std::fmt::Debug`
 --> src/main.rs:3:26
  |
1 | fn foo(constraints: impl Iterator) {
  |                                    - help: consider further restricting the associated type: `where <impl Iterator as std::iter::Iterator>::Item: std::fmt::Debug`
2 |     for constraint in constraints {
3 |         println!("{:?}", constraint);
  |                          ^^^^^^^^^^ `<impl Iterator as std::iter::Iterator>::Item` cannot be formatted using `{:?}` because it doesn't implement `std::fmt::Debug`
  |
  = help: the trait `std::fmt::Debug` is not implemented for `<impl Iterator as std::iter::Iterator>::Item`
  = note: required by `std::fmt::Debug::fmt`
```

which is incorrect as `where <impl Iterator as std::iter::Iterator>::Item: std::fmt::Debug` is not valid syntax nor would it restrict the positional `impl Iterator` parameter if it were.

The output being introduced is

```
error[E0277]: `<impl Iterator as std::iter::Iterator>::Item` doesn't implement `std::fmt::Debug`
 --> src/main.rs:3:26
  |
3 |         println!("{:?}", constraint);
  |                          ^^^^^^^^^^ `<impl Iterator as std::iter::Iterator>::Item` cannot be formatted using `{:?}` because it doesn't implement `std::fmt::Debug`
  |
  = help: the trait `std::fmt::Debug` is not implemented for `<impl Iterator as std::iter::Iterator>::Item`
  = note: required by `std::fmt::Debug::fmt`
help: introduce a type parameter with a trait bound instead of using `impl Trait`
   |
LL | fn foo<T: Iterator>(constraints: T) where <T as std::iter::Iterator>::Item: std::fmt::Debug  {
   |       ^^^^^^^^^^^^^              ^  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```

This suggestion is correct and lead the user in the right direction: because you have an associated type restriction you can no longer use `impl Trait`, the only reasonable alternative is to introduce a named type parameter, bound by `Trait` and with a `where` binding on the associated type for the new type parameter `as Trait` for the missing bound.

*Ideally*, we would want to suggest something like the following, but that is not valid syntax today

```
error[E0277]: `<impl Iterator as std::iter::Iterator>::Item` doesn't implement `std::fmt::Debug`
 --> src/main.rs:3:26
  |
3 |         println!("{:?}", constraint);
  |                          ^^^^^^^^^^ `<impl Iterator as std::iter::Iterator>::Item` cannot be formatted using `{:?}` because it doesn't implement `std::fmt::Debug`
  |
  = help: the trait `std::fmt::Debug` is not implemented for `<impl Iterator as std::iter::Iterator>::Item`
  = note: required by `std::fmt::Debug::fmt`
help: introduce a type parameter with a trait bound instead of using `impl Trait`
   |
LL | fn foo(constraints: impl Iterator<Item: std::fmt::Debug>) {
   |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```

Fix #69638.

The compiler normalizes source when reading files initially (removes BOMs, etc), but not when loading external sources.

Fixes #70874 by normalizing when loading external sources too. Adds a test to verify normalization.

rustc: Add a warning count upon completion

This adds a `build completed with one warning/x warnings` message, similar to the already present `aborted due to previous error` message.