[Polly][OpTree] Better report applied changes.

Print to dbgs() any taken action.

Also, read-only scalars do not require any action unless
-polly-analyze-read-only-scalars=true is used. Better refect this by
using ForwardingAction::triviallyForwardable and thus not bumping the
statistics.
GitOrigin-RevId: c1cf51e77701719f3439eed148dfaf44e726c586
2 files changed