[llvm] [CrossDSO CFI] Make sure __cfi_check has BTI attribute. (PR #131224)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

I'm not confident this patch is the best solution, but I'm not sure what a better solution looks like; should clang be setting the relevant function attributes somehow?

https://github.com/llvm/llvm-project/pull/131224