OpenCV_Contrib builds in java with empty modules

Question

I have cross-compiled the opencv_contrib modules with opencv (contrib github, opencv github) from c++ to java using cmake and the mingw cross compiler, but some of the built modules (line_descriptors and DPM) built as empty classes or classes with no usable methods. I could not find anyone else with the same problem, which suggests that I am doing something completely wrong in my build. I followed this guide, but also disabled precompiled headers and commented out "#include reg.hpp" in reg.cpp and "#include datasets.hpp" in datasets.cpp. I can post my cmakevars file if needed, but I thought that might take up too much room.