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

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

I think using cmakedefine01 is an improvement. As far as splitting every option into its own header, I've never wanted to dynamically flip between these. These mostly look like the kind of options I'd be surprised would even work to change after setting once in the CMakeCache. 

Isn't there an additional cost to reading N smaller files?

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