Many LLVM transformations benefits from knowing the targets. This enables optimizations, especially in a JIT context when the target is (generally) well-known. Closes #49 COPYBARA_INTEGRATE_REVIEW=https://github.com/tensorflow/mlir/pull/49 from dcaballe:dcaballe/tti ab02f72eb326f660945696e5dadeeb983cf263b3 PiperOrigin-RevId: 261840617