[llvm] [LTO] Set default Darwin CPU to apple-a7 for AArch64 (PR #81540)

[Jon Roelofs via llvm-commits]

https://github.com/jroelofs commented:

> I think `cyclone` and `apple-a7` is the same CPU (see `AArch64.td`).

Yes.

> If we are going to rename default to a well-known name, might as well rename aarch64_32 as well.

Agreed. We should prefer the `apple-a*` names over their weather-event-ish aliases.

https://github.com/llvm/llvm-project/pull/81540