[llvm] [clang] [RISCV] Implement shadow stack on shadow stack mode with Zicfiss. (PR #68075)

[Yeting Kuo via cfe-commits]

yetingk wrote:

Unwinder could use property `GNU_PROPERTY_RISCV_FEATURE_1_ZICFISS` to know the binary uses `ssp` as the shadow stack register.
https://github.com/riscv-non-isa/riscv-elf-psabi-doc/pull/417/files

https://github.com/llvm/llvm-project/pull/68075