[llvm] [mlir] Introduce LDBG_OS() macro as a variant of LDBG() (PR #157194)

[Mehdi Amini via llvm-commits]

joker-eph wrote:

Working with @math-fehr and iterating on the implementation, I managed to simplify if further in this last push: https://github.com/llvm/llvm-project/compare/13b70c3611f1bc49191698c8ddd52a74c81f5201..8b8b41a5157645de0addc70869e2d5d8e5a9cb57

https://github.com/llvm/llvm-project/pull/157194