Suppress unused variables warnings in release mode

[mkoval]

Building DART in release mode disables assertions. There are a few parameters in DART that are only used in assertions, so this generates -Wunused-parameter warnings. This pull request adds a DART_UNUSED that suppresses those warnings. See this StackOverflow answer for more explanation.

[jslee02]

👍

[psigen]

It seems a bit strange to require arguments that are only used in assertions.

Are these parameters required as part of some standardized spec? Is there a reason we force them to be passed when they are apparently not strictly necessary for the function?

[jslee02]

This is a reasonable concern.

In DartTNLP case, we should follow the same function prototype as it overrides Ipopt::TNLP functions. We could comment out, but I would like to leave _m uncommented to be used in the assertion for debugging purpose (checking the dimensionality).

We could remove _numDir for ODELCPSolver case. One thing we should note is that this class isn't used anywhere (at least in our code base) so I would be fine to remove _numDir. Personally, I'm a bit inclined to leave it until we decide whether remove this unused class ODELCPSolver or improve to use somewhere. I think at some point we need to refactor the constraint solving and can figure out what we will do with ODELCPSolver at that moment.