[llvm] [RISCV][Zicfilp] Emit .note.gnu.property section for Zicfilp CFI unlabeled scheme (PR #141468)

[Nemanja Ivanovic via llvm-commits]

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nemanjai wrote:

Should this be `llvm_unreachable`? Seems like this is something an IR-producer can easily trigger without any internal code inconsistency in LLVM. This seems to me like it would be more appropriate to use `repor_fatal_error` here.

https://github.com/llvm/llvm-project/pull/141468