Rollup merge of #124090 - durin42:llvm-19-riscv-feature, r=cuviper

llvm: update riscv target feature to match LLVM 19

In llvm/llvm-project@9067070 they ended up largely reverting
llvm/llvm-project@e817966. This means the change we did in
rust-lang/rust@b378059 is now only corrct for LLVM 18...so we have to adjust again.

``@rustbot`` label: +llvm-main

Author: matthiaskrgr