[llvm] [mlir] Shard the public llvm-config.h in multiple files (NFC) (PR #71273)

[Chris B via llvm-commits]

llvm-beanz wrote:

Adding new files for new options and splitting defines across a bunch of files is messy and will incur maintenance as people have a whole bunch of files floating around. Which isn't to say we shouldn't do this, but have you benchmarked how much this can improve build times? This is a lot of complexity to add to our includes and build settings system if it doesn't have a significant benefit.

https://github.com/llvm/llvm-project/pull/71273