According to the Apple developer docs:

> The type va_list is an alias for char * rather than for the struct
> type specified in the generic PCS.

The current implementation uses the generic Aarch64 structure for VaList
for Aarch64 iOS.

Windows always uses the char * variant of the va_list.

…henkov

Suggest an appropriate token when encountering `pub Ident<'a>`

Fix rust-lang#55403. Follow up to rust-lang#45997.

Improve the usage message for `-Z dump-mir`.

Ouput now looks like this:
```
$ rustc -Z help
...
    -Z               arg-align-attributes -- emit align metadata for reference arguments
    -Z                       dump-mir=val -- dump MIR state to file.
        `val` is used to select which passes and functions to dump. For example:
        `all` matches all passes and functions,
        `foo` matches all passes for functions whose name contains 'foo',
        `foo & ConstProp` only the 'ConstProp' pass for function names containing 'foo',
        `foo | bar` all passes for function names containing 'foo' or 'bar'.
    -Z                   dump-mir-dir=val -- the directory the MIR is dumped into
...
```

Fixes rust-lang#56558

codegen: Fix va_list - aarch64 iOS/Windows

## Summary

Fix code generated for `VaList` on Aarch64 iOS/Windows.

## Details

According to the [Apple - ARM64 Function Calling Conventions]:

> ... the type va_list is an alias for char * rather than for the struct
> type specified in the generic PCS.

The current implementation uses the generic Aarch64 structure for `VaList`
for Aarch64 iOS. Switch to using the `char *` variant of the `VaList`
and use the corresponding `emit_ptr_va_arg` for the `va_arg` intrinsic.

Windows always uses the `char *` variant of the `VaList`. Update the `va_arg`
intrinsic to use `emit_ptr_va_arg`.

[Apple - ARM64 Function Calling Conventions]: https://developer.apple.com/library/archive/documentation/Xcode/Conceptual/iPhoneOSABIReference/Articles/ARM64FunctionCallingConventions.html

Fix the just-introduced ptr::hash docs

Follow-up to rust-lang#56250.

resolve: Reduce some clutter in import ambiguity errors

Noticed in https://www.reddit.com/r/rust/comments/a3pyrw/announcing_rust_131_and_rust_2018/eb8alhi/.
The first error is distracting, but unnecessary, it's a *consequence* of the ambiguity error and appears because one of the ambiguous `actix` modules (unsurprisingly) doesn't have the expected name in it.

…=Centril

Add missing comma in Generators