[clang] [llvm] [RISCV] Add NutShell RV32/64 processors definition (PR #102899)

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owlxiao wrote:

> Some relevant context for what CPUs we permit merging into LLVM: [#102452 (comment)](https://github.com/llvm/llvm-project/pull/102452#issuecomment-2275962014)
> 
> How does this apply to NutShell?

I'm sorry to see this. I will handle it manually once Hazard3 is merged into the mainline.

https://github.com/llvm/llvm-project/pull/102899