[llvm] [AArch64] Make IFUNC opt-in rather than opt-out. (PR #171648)

[Harald van Dijk via llvm-commits]

hvdijk wrote:

> I made that suggestion because if a target supports both it doesn't matter what we do.

Thanks. Sure, if a target supports both, either would work, but are they equally good? I would have thought that a PAuth relocation would be better in that case, because an IFUNC relocation effectively re-creates logic that the loader has already. But I don't feel strongly about it and it would still unblock us to do it that way, so I will make that change, it will just require some additional test updates where the result is then intended be different.

https://github.com/llvm/llvm-project/pull/171648