Rollup merge of #139440 - a4lg:riscv-feature-addition-batch-2, r=Amanieu

rustc_target: RISC-V: feature addition batch 2

Of ratified RISC-V extensions, this commit adds ones satisfying following criteria:

1.  Either discoverable through a `riscv_hwprobe` system call on Linux 6.14
    or should be very helpful even on basic needs (the `B` extension),
2.  Does not disrupt current Rust's feature handling mechanism and
3.  Not too OS-dependent (the `Supm` extension)

Due to 2., the author excluded `Zcf` (RV32 only) and `Zcd` from the list despite that they are discoverable from Linux 6.14.

Due to 3., the author excluded the `Supm` extension on the PR version 2.

This is based on the specification:
*   [The latest ratified ISA Manuals (version 20240411)](https://lf-riscv.atlassian.net/wiki/spaces/HOME/pages/16154769/RISC-V+Technical+Specifications)

Linux Definition: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/riscv/include/uapi/asm/hwprobe.h

LLVM Definitions:

*   [`B`](https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/RISCV/RISCVFeatures.td#L507-L510)
*   [`Zca`](https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/RISCV/RISCVFeatures.td#L395-L398)
*   [`Zcb`](https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/RISCV/RISCVFeatures.td#L407-L410)
*   [`Zcmop`](https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/RISCV/RISCVFeatures.td#L460-L463)
*   [`Zfa`](https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/RISCV/RISCVFeatures.td#L335-L338)
*   [`Zicboz`](https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/RISCV/RISCVFeatures.td#L89-L92)
*   [`Zicond`](https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/RISCV/RISCVFeatures.td#L125-L128)
*   [`Zihintntl`](https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/RISCV/RISCVFeatures.td#L148-L151)
*   [`Zimop`](https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/RISCV/RISCVFeatures.td#L161-L162)
*   [`Ztso`](https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/RISCV/RISCVFeatures.td#L214-L217)

The author also adds required implication: `C` implies `Zca`.

Android RISC-V target is also updated to include the `B` extension (this is just a shorthand combination of `Zba`, `Zbb` and `Zbs` extensions but possibly simplifies `target_feature` handling).

# History

## Version 1 → 2

*   Remove the `Supm` extension from the Rust target features (thanks, `@Amanieu).`

--------

Related:
*   #44839
    (`riscv_target_feature`)
*   #138823
    (my previous batch)
*   #132618
    (stabilization of the `Zfa` extension is blocked by this)

`@rustbot` r? `@Amanieu`
`@rustbot` label +T-compiler +O-riscv +A-target-feature

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