Support can be determined by checking for the "d32" LLVM feature.

Continuation of rust-lang#94376.

cc rust-lang#53667

…olnay

Add a `process_group` method to UNIX `CommandExt`

- Tracking issue: rust-lang#93857
- RFC: rust-lang/rfcs#3228

Add a `process_group` method to `std::os::unix::process::CommandExt` that
allows setting the process group id (i.e. calling `setpgid`) in the child, thus
enabling users to set process groups while leveraging the `posix_spawn` fast
path.

ARM: Only allow using d16-d31 with asm! when supported by the target

Support can be determined by checking for the "d32" LLVM feature.

r? `@nagisa`

…henkov

Improve allowness of the unexpected_cfgs lint

This pull-request improve the allowness (`#[allow(...)]`) of the `unexpected_cfgs` lint.

Before this PR only crate level `#![allow(unexpected_cfgs)]` worked, now with this PR it also work when put around `cfg!` or if it is in a upper level. Making it work ~for the attributes `cfg`, `cfg_attr`, ...~ for the same level is awkward as the current code is design to give "Some parent node that is close to this macro call" (cf. https://doc.rust-lang.org/nightly/nightly-rustc/rustc_expand/base/struct.ExpansionData.html) meaning that allow on the same line as an attribute won't work. I'm note even sure if this would be possible.

Found while working on rust-lang#94298.
r? `@petrochenkov`

…an-DPC

7 - Make more use of `let_chains`

Continuation of rust-lang#94376.

cc rust-lang#53667

compiler: fix some typos