[clang] [llvm] [RISCV] Implement the implications of C extension (PR #132259)

[Sam Elliott via cfe-commits]

https://github.com/lenary commented:

I commented about the predicates (before i saw the other comments). I thought they'd be ok to do in a follow-up, but you should just to the refactoring now as it won't quite be NFC as I expected.

https://github.com/llvm/llvm-project/pull/132259