[llvm] [GitHub][RISCV] Restrict backend:RISC-V labelling to Clang and LLVM (PR #192429)

[Luke Lau via llvm-commits]

lukel97 wrote:

> What about lld? Those changes generally would be specific to RISC-V.

Are they specific to the LLVM RISC-V backend though? I would have thought those interested in those changes would have subscribed to the lld label. But happy to add it in if we think there's enough overlap between developers.

https://github.com/llvm/llvm-project/pull/192429