COMP: error out early if OpenCV is disabled but required

...earning/Supervised/include/otbBoostMachineLearningModel.h

.../Supervised/include/otbBoostMachineLearningModelFactory.h

.../Supervised/include/otbDecisionTreeMachineLearningModel.h

...ised/include/otbDecisionTreeMachineLearningModelFactory.h

...ised/include/otbGradientBoostedTreeMachineLearningModel.h

...clude/otbGradientBoostedTreeMachineLearningModelFactory.h

...rvised/include/otbKNearestNeighborsMachineLearningModel.h

...include/otbKNearestNeighborsMachineLearningModelFactory.h

...Supervised/include/otbNeuralNetworkMachineLearningModel.h

...sed/include/otbNeuralNetworkMachineLearningModelFactory.h

...g/Supervised/include/otbNormalBayesMachineLearningModel.h

...vised/include/otbNormalBayesMachineLearningModelFactory.h

...Supervised/include/otbRandomForestsMachineLearningModel.h

...sed/include/otbRandomForestsMachineLearningModelFactory.h

Modules/Learning/Supervised/include/otbRequiresOpenCVCheck.h

.../Learning/Supervised/include/otbSVMMachineLearningModel.h

...ng/Supervised/include/otbSVMMachineLearningModelFactory.h