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

[Frank Schlimbach via llvm-commits]

fschlimb wrote:

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

Ok, I overlooked. Thanks. Fixed now.

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