[clang] [llvm] [mlir] [CMake] Make find_package(Clang) load MLIR when ClangIR uses a full MLIR (PR #228366)

[Erich Keane via cfe-commits]

erichkeane wrote:

I honestly have no idea here, I know nothing of cmake.    I'm hopeful you can find a better reviewer than me.

https://github.com/llvm/llvm-project/pull/228366