[llvm] [clang] [RISCV] Add Zicfiss support to the shadow call stack implementation. (PR #68075)

[Yeting Kuo via cfe-commits]

yetingk wrote:

> Will [riscv-non-isa/riscv-elf-psabi-doc#417](https://github.com/riscv-non-isa/riscv-elf-psabi-doc/pull/417) be implemented in a separate patch?

Sure.

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