[clang] [llvm] [RISCV] Teach .option arch to support experimental extensions. (PR #89727)

[Paul T Robinson via cfe-commits]

pogo59 wrote:

Driver tests are supposed to verify Driver behavior. That is, use `-###` and make sure the correct option is being passed down to the compiler. They should not be compiling anything.

https://github.com/llvm/llvm-project/pull/89727