[llvm] [mlir] eliminating g++ warnings (PR #105520)

[Jakub Kuderski via llvm-commits]

kuhar wrote:

> Rebased. @dwblaikie @arsenm @joker-eph @kuhar Any other comments? Can this be merged?

I can still see the `[[maybe_unused]]` attributes in https://github.com/llvm/llvm-project/pull/105520#discussion_r1728608021 and https://github.com/llvm/llvm-project/pull/105520#discussion_r1728608995. I thought we wouldn't need them after the cmake change?

https://github.com/llvm/llvm-project/pull/105520