PR #15928 made `Checking` and `Building` the same style because the
transient state is `note:` and #15928 made `note:~ the same as our
regular headers.

This switches the transient state to `help:` until we can further
explore color choices with rustc.

See also https://rust-lang.zulipchat.com/#narrow/channel/246057-t-cargo/topic/colors.20removed.20in.201.2E91.20.28current.20beta.29.3F/near/541900531

…6020)

Beta backports
- b486362
- rust-lnag/cargo@92182d4
- d33f651 

In order to make CI pass, the following PRs are also cherry-picked:

---

Addresses a usability issue fixed in #16019

Unclear why it wasn't missing before.

The line was added five years ago.
Seems it should be available.
https://github.com/actions/runner-images/blob/75ec4229/images/ubuntu/scripts/build/install-rust.sh#L19-L20

Maybe due to recent pin/unpin 1.89 issue?
actions/runner-images@69c94f5b

The test exercises a regression of extra `-Zbuild-std-features`
overriding the entire default-features set.
However, after rust-lang/rust 146317 panic_immediate_abort
became a codegen flag not a Cargo feature anymore.
We pick another `optimize_for_size` feature flag to ensure the
regression case is still covered.

To verify `optimize_for_size` actually triggers the regression,
git revert f004691
and changes to `-Zbuild-std-features=optimize_for_size`.

Alternatively, we can just drop this test.

…6050)

Beta backports
- e906ad9 (ignoring
flaky test otherwise it sometimes fails rust-lang/rust beta backport)

In order to make CI pass, the following PRs are also cherry-picked:

- b6d572b
- c249c45

This was an overlook in 1891593
that forgot to replace other `rmeta_x`.

#16057)

Beta backports
- 129593d

In order to make CI pass, the following PRs are also cherry-picked:

The "host" string is ambiguous

* We have `-Zhost-config` that config `[host]` table applies to
  artifacts running on host, such as build scripts and proc macros.
* `host` sounds like the default behavior, whereas `--target host`
  is in the cross-compilation mode: `target/<triple>/debug`.
* We might want to reserve `host` for future use

Beta backports
- a5c8b96

In order to make CI pass, the following PRs are also cherry-picked: