RISC-V: Remove footnote from the Zcb extension

[a4lg]

This commit removes excess footnote caused by sloppy copy-and-paste of other Zc* extension lines (the footnote is true for other currently supported Zc? extensions but not Zcb).

[rustbot]

r? @Amanieu

rustbot has assigned @Amanieu.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[a4lg]

Converted to draft due to this: rust-lang/rust#140389 (comment)

[sayantn]

The CI failures are due to a rustc fix, #1788 also fixes them

[a4lg]

I can understand that CI failures on stdarch (alone) are fixed by #1788.
However, I cannot believe that all CI failures on Rust side (rust-lang/rust#140389) are fixed by that.

[sayantn]

All the errors are fixed, I have rebased after merge of #1788. Only errors are these rustdoc ones (afaik the doc link checks are the very last step of the CI, so I am pretty sure nothing else is wrong).

The CI failures in stdarch and rustc had different origins, the rustc CI failed because some of the avx512fp16 intrinsic implementations were using avx512vl intrinsics, which the PR forbids. The stdarch CI was failing due to a rustc fix which stopped emitting align attributes to parameters for x86-32 msvc

[sayantn]

Also, please rebase as the fix has been merged, so now the CI should pass

[a4lg]

@sayantn I understand that (BTW, I rebased it) and rustdoc CI error on the Rust side is exactly what I'm talking about (why this change should not be merged for now; I'm closing this in parity with #1792).

I received pretty good responses for rust-lang/rust#140434 (that will make my changes not an error). However, even if this is merged to master in a regular path, CI detected doc errors using the stage0 compiler (in the Beta channel), meaning we have to wait the next beta to merge this (and #1779) for Nightly.

[sayantn]

Ok that makes sense. Isn't the bootstrap bump near? Anyway I will be testing the PR by reverting the stdarch doc PR on a private branch

[a4lg]

@sayantn

Isn't the bootstrap bump near?

Because stage0 compiler is in the beta channel, being merged into the master (the nightly channel) at the time when the bootstrap compiler bump happens is insufficient (beta backporting is an exception for this but usually restricted for regressions).

What really concerns me and the keyword "near" is related, is the planned branching date (between 1.88-beta and 1.89-nightly; around May 9, 2025).
If rust-lang/rust#140434 doesn't make it to the 1.88-beta, I have to wait another version cycle to restore #1779.