Rollup merge of #130877 - taiki-e:riscv-atomic, r=Amanieu ...
rustc_target: Add RISC-V atomic-related features
This adds the following three target features to unstable riscv_target_feature.
- `zaamo` (Zaamo Extension 1.0.0): Atomic Memory Operations (`amo*.{w,d}{,.aq,.rl,.aqrl}`)
([definition in LLVM](https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/RISCV/RISCVFeatures.td#L229-L231 ), [available since LLVM 19](8be079cdddhttps://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/RISCV/RISCVFeatures.td#L238-L240 ), [available since LLVM 19](6b7444964ahttps://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/RISCV/RISCVFeatures.td#L261-L263 ), [available since LLVM 19](8be079cddd70e7d26e56614aeda93be87412e62108693e29ec/gcc/config/riscv/arch-canonicalize (L44)https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/RISCV/RISCVFeatures.td#L206 ).
- Zabha and Zaamo are in a similar situation, [riscv-isa-manual](https://github.com/riscv/riscv-isa-manual/blob/main/src/zabha.adoc ) says "The Zabha extension depends upon the Zaamo standard extension", and [`zabha` implies `zaamo` in GCC](08693e29ec/gcc/config/riscv/arch-canonicalize (L45-L46)https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/TargetParser/RISCVISAInfo.cpp#L776-L778 ).
r? `@Amanieu`
`@rustbot` label +O-riscv +A-target-feature
acaa6cee07