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

[Eleanor Bonnici via llvm-commits]

eleanor-arm wrote:

I made a similar change to https://github.com/llvm/llvm-project/pull/81020 and it now passes the IR tests just like https://github.com/llvm/llvm-project/pull/81020. However, if the register is forced in integrated assembly this fix doesn't work (and neither does  https://github.com/llvm/llvm-project/pull/81020 I don't think. It looks like clang doesn't translate this to correct IR. 

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