[libcxx-commits] [libcxx] [libc++] Split up ABI and platform configuration to their own headers (PR #90863)

[Louis Dionne via libcxx-commits]

ldionne wrote:

Put differently: I want to split out ABI macros so I can improve that system without things getting out of hand inside `__config`, but I can't do that unless I also split out the platform configuration from `__config` because I run into circular dependencies otherwise. So my goal is not to split as much as possible, it's to do the minimum split that makes sense to get ABI macros out of `__config`.

https://github.com/llvm/llvm-project/pull/90863