[clang] [llvm] [AArch64] set AppleA14 architecture version to v8.4-a (PR #92600)

[Jon Roelofs via cfe-commits]

jroelofs wrote:

> @jroelofs on a slight tangent, when do we get to add information on the M4 chip?

https://github.com/llvm/llvm-project/pull/95478

https://github.com/llvm/llvm-project/pull/92600