Tracking: RISC-V platform guide documentation

[a4lg]

#1779 is once merged but reverted by #1792.

This is because rustdoc does not support multiple references to a single footnote and generates HTML with duplicate IDs (although no warnings will be generated).
The author proposed rust-lang/rust#140434 to enable writing such references without creating elements with the same ID.

Note: std_detect is moved to the main Rust repository (so technically, stdarch is no longer relevant) but I'll keep tracking this issue on stdarch.

TODO

Requirements (repository=rust)

• rustdoc: Allow multiple references to a single footnote rust#140434 is merged.
• stage0 (bootstrap) compiler is bumped and bumped compiler contains the change above.
  This might not be necessary since std_detect is moved to the main Rust repository (needs trying).

What to do

• repository=rust: Re-apply [RFC] std_detect: RISC-V platform guide documentation #1779 with updates (including RISC-V: Remove footnote from the Zcb extension #1789)

cc: @sayantn

[a4lg]

Note: std_detect is moved to the main Rust repository (so technically, stdarch is no longer relevant) but I'll keep tracking this issue on stdarch.