When you attempt to access MIDIDeviceController.h in your own project, it'll fail when you include it. This is the main error, while the other is a syntax error:
missing type specifier - int assumed. Note: C++ does not support default-int
While this didn't occur in 4.13, it's due to the plugin in question being added in 4.14
Head over to the existingAnswerHub thread and let us know what's up.