[clang] [llvm] [RISCV] Add Propeller support for RISC-V (PR #170992)

[Pengcheng Wang via llvm-commits]

https://github.com/wangpc-pp commented:

Thanks! We are interested in this work!

There are some suggestions:
1.  Please add some tests for these driver changes.
3. Can you describe what we are missing for the support of Propeller in the middle/back ends? For example, I don't know the relationship between Propeller and `insertNoop`.
4. Can you show the current status and the state after your changes? Have you tried it on real hardware and do we need anything else to make Propeller work?

https://github.com/llvm/llvm-project/pull/170992