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

[Steven Wu via llvm-commits]

cachemeifyoucan wrote:

I think `cyclone` and `apple-a7` is the same CPU (see `AArch64.td`). If we are going to rename default to a well-known name, might as well rename aarch64_32 as well.

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