…-facing linker flavors

Remove one unstable user-facing linker flavor (l4-bender)

There are times where computing a value may be cheap, or where
computing a reference may be expensive, so this fills out the
possibilities.

…ref_of}`

While the `provide_*` methods already short-circuit when a value has
been provided, there are times where an expensive computation is
needed to determine if the `provide_*` method can even be called.

Before, the MIR validator used RevealAll in its ParamEnv for type
checking. This could cause false negatives in some cases due to
RevealAll ParamEnvs not always use all predicates as expected here.

Since some MIR passes like inlining use RevealAll as well, keep using
it in the MIR validator too, but when it fails usign RevealAll, also
try the check without it, to stop false negatives.

Before, it called `normalize_erasing_regions` twice since
`equal_up_to_regions` called it as well for both types.

`std::os::fd` defines types like `OwnedFd` and `RawFd` and is common
between Unix and non-Unix platforms that share a basic file-descriptor
concept. Rust currently uses this internally to simplify its own code,
but it would be useful for external users in the same way, so make it
public.

This means that `OwnedFd` etc. will all appear in three places, for
example on unix platforms:
 - `std::os::fd::OwnedFd`
 - `std::os::unix::io::OwnedFd`
 - `std::os::unix::prelude::OwnedFd`

Add `#[unstable(feature = "os_fd", issue = "98699")]` to the new
`pub use` declarations.

Walkthrough currently say:

```
rustup target add aarch_64-fuchsia
```
but should say

```
rustup target add aarch64-fuchsia
```

The impl-items list stopped being nested inside a docblock since c1b1d68

…r=joshtriplett

Make `std::os::fd` public.

`std::os::fd` defines types like `OwnedFd` and `RawFd` and is common
between Unix and non-Unix platforms that share a basic file-descriptor
concept. Rust currently uses this internally to simplify its own code,
but it would be useful for external users in the same way, so make it
public.

This means that `OwnedFd` etc. will all appear in three places, for
example on unix platforms:
 - `std::os::fd::OwnedFd`
 - `std::os::unix::io::OwnedFd`
 - `std::os::unix::prelude::OwnedFd`

r? ```@joshtriplett```

Add additional methods to the Demand type

This adds on to the original tracking issue rust-lang#96024

r? ```@yaahc```

… r=oli-obk

Try normalizing types without RevealAll in ParamEnv in MIR validation

Before, the MIR validator used RevealAll in its ParamEnv for type
checking. This could cause false negatives in some cases due to
RevealAll ParamEnvs not always use all predicates as expected here.

Since some MIR passes like inlining use RevealAll as well, keep using
it in the MIR validator too, but when it fails usign RevealAll, also
try the check without it, to stop false negatives.

Fixes rust-lang#99866

cc ``@compiler-errors`` who nicely helped me on zulip

…imulacrum

Change implementation of `-Z gcc-ld` and `lld-wrapper` again

This PR partially reverts rust-lang#97375 and uses the strategy described in rust-lang#97402 (comment) instead, thus fixes rust-lang#97755.

rustc_target: Add a compatibility layer to separate internal and user-facing linker flavors

I want to do some refactorings in `rustc_target` - merge `lld_flavor` and `linker_is_gnu` into `linker_flavor`, support combination gcc+lld (rust-lang#96827).
This PR adds some compatibility infra that makes that possible without making any changes to user-facing interfaces - `-Clinker-flavor` values and json target specs. (For json target specs this infra may eventually go away since they are not very stable.)

The second commit does some light refactoring of internal linker flavors (applies changes from petrochenkov@53eca42 that don't require mass-editing target specs).

…henkov

Add warning against unexpected --cfg with --check-cfg

This PR adds a warning when an unexpected `--cfg` is specified but not in the specified list of `--check-cfg`.

This is the follow-up PR I mentioned in rust-lang#99519.

r? ```@petrochenkov```

…re-whitespace, r=notriddle

Remove unneeded where whitespace

It fixes these two bugs:

![Screenshot from 2022-08-31 18-14-40](https://user-images.githubusercontent.com/3050060/187727950-94657419-abfa-454c-9d27-004280fbcb45.png)
![Screenshot from 2022-08-31 18-14-49](https://user-images.githubusercontent.com/3050060/187727956-21d1b39d-62d7-4e7b-8f6f-631ceda67a19.png)

It's a relic from a very old time (this commit: rust-lang@bfd01b7).

You can test the result [here](https://rustdoc.crud.net/imperio/remove-unneeded-where-whitespace/lib2/struct.WhereWhitespace.html).

cc ```@jsha```
r? ```@notriddle```

Fix  bad target name in Walkthrough

Walkthrough currently say:

```
rustup target add aarch_64-fuchsia
```
but should say

```
rustup target add aarch64-fuchsia
```

…re-css, r=jsha

rustdoc: remove unused `.docblock .impl-items` CSS

The impl-items list stopped being nested inside a docblock since c1b1d68

… r=tmandry

Fixes/adjustments to Fuchsia doc walkthrough

Small fixes/adjustments missed during rust-lang#100927