onnxruntime

add maybe unused attribute to vars only used for logging (#15970)

### Description
Add maybe_unused attribute to variables that are only used for logging



### Motivation and Context
Building ORT with training using Xcode 14.3 causes`
-Wunused-but-set-variable` error as some variables are created and
exclusively used for debug logging. Adding maybe_unused suppresses
warnings on unused variables when logging is disabled and fixes the
local build.