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

[Yeting Kuo via cfe-commits]

yetingk wrote:

I fix the issue by using feature to control the permission of experimental extension.

> Does this disable use of experimental extensions for a `.option arch` in an inline assembly block without -menable-experimental-extensions.



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