The `error reading rustc version` message could be improved

Problem

M1 macOS 12.4.1

> rustup update
info: syncing channel updates for 'stable-aarch64-apple-darwin'
info: syncing channel updates for 'stable-x86_64-unknown-linux-gnu'
info: syncing channel updates for 'nightly-aarch64-apple-darwin'
info: checking for self-update

      stable-aarch64-apple-darwin unchanged - rustc 1.75.0 (82e1608df 2023-12-21)
  stable-x86_64-unknown-linux-gnu unchanged - (error reading rustc version)
     nightly-aarch64-apple-darwin unchanged - rustc 1.77.0-nightly (89e2160c4 2023-12-27)

Steps

rustup update with stable-x86_64-unknown-linux-gnu toolchain

Possible Solution(s)

No response

Notes

No response

Rustup version

rustup 1.26.0 (5af9b9484 2023-04-05)
info: This is the version for the rustup toolchain manager, not the rustc compiler.
info: The currently active `rustc` version is `rustc 1.75.0 (82e1608df 2023-12-21)`

### Installed toolchains

```console
Default host: aarch64-apple-darwin
rustup home:  /Users/foobar/.rustup

installed toolchains
--------------------

stable-aarch64-apple-darwin (default)
stable-x86_64-unknown-linux-gnu
nightly-aarch64-apple-darwin
1.60.0-aarch64-apple-darwin
1.61.0-aarch64-apple-darwin
1.65.0-aarch64-apple-darwin
1.70.0-aarch64-apple-darwin

installed targets for active toolchain
--------------------------------------

aarch64-apple-darwin
aarch64-unknown-linux-gnu
x86_64-pc-windows-msvc

active toolchain
----------------

stable-aarch64-apple-darwin (default)
rustc 1.75.0 (82e1608df 2023-12-21)

Begin with the rustup update command and the stable-x86_64-unknown-linux-gnu toolchain case described in the report. Trace how the “error reading rustc version” line is produced; done means the failure reports a more useful message, with regression coverage for the reported case.