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

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

I don't think the inline asm is actually necessary to reproduce the issue, it just makes it easier to write a small testcase by controlling the behavior of the register allocator.

> The fix code is not run when compiling any C/C++ testcases I have available with Aarch64 target. 

I'm not sure what you're referring to here.  The important change is the change to AArch64InstrInfo.td.

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