Auto merge of #138947 - madsmtm:refactor-apple-versions, r=Noratrieb

Refactor Apple version handling in the compiler

Move various Apple version handling code in the compiler out `rustc_codegen_ssa` and into a place where it can be accessed by `rustc_attr_parsing`, which I found to be necessary when doing rust-lang/rust#136867. Thought I'd split it out to make it easier to land, and to make further changes like rust-lang/rust#131477 have fewer conflicts / PR dependencies.

There should be no functional changes in this PR.

`@rustbot` label O-apple
r? rust-lang/compiler

Author: bors