[clang] [CMake] Disable CIR in the Apple caches (PR #235165)

[Erich Keane via cfe-commits]

erichkeane wrote:

> LGTM.
> 
> FWIW, the MLIR dependency isn't the only reason to disable CIR. IMO, we also aren't prepared for the build-time hit & would also want to observe (maybe measure is the better word?) more concrete benefits to client compilations. Perhaps that should be mentioned in the commit message.

I posted a response on the other thread for fushia, but this is disappointing. We are quickly starting to add benefit in the near future, and this will result in apple platforms not being able to get those well tested. Progress has been made on build times (with some gated on the cmake update), so hopefully the pain will be short term.

https://github.com/llvm/llvm-project/pull/235165