[clang] [RISCV] Disable generation of asynchronous unwind tables for RISCV baremetal (PR #81727)

[Fangrui Song via cfe-commits]

MaskRay wrote:

I wonder whether GCC considers using `-fno-asynchronous-unwind-tables` for all RISC-V configurations.

https://github.com/llvm/llvm-project/pull/81727