[llvm] Do not use R12 for indirect tail calls with PACBTI (PR #82661)

[Eleanor Bonnici via llvm-commits]

eleanor-arm wrote:

Actually the problem looks quite simple. When compiling with `-mbranch-protection=standard`, I'd expect to see `"sign-return-address"="all"` as one of the function attributes in the IR but it's not there. 

https://github.com/llvm/llvm-project/pull/82661