This is stuff I have also entered as an issue on the GitHub issue log. There is more information there.

D:\cabbage-master\Builds\Windows>g++.exe -shared -Wl,--dll -o build\CabbagePluginSynth.dat build\intermediate\Debug\juce_audio_basics.o build\intermediate\Debug\juce_audio_devices.o build\intermediate\Debug\juce_audio_formats.o build\intermediate\Debug\juce_audio_processors.o build\intermediate\Debug\juce_audio_utils.o build\intermediate\Debug\juce_core.o build\intermediate\Debug\juce_cryptography.o build\intermediate\Debug\juce_data_structures.o build\intermediate\Debug\juce_events.o build\intermediate\Debug\juce_graphics.o build\intermediate\Debug\juce_gui_basics.o build\intermediate\Debug\juce_gui_extra.o build\intermediate\Debug\juce_PluginUtilities.o build\intermediate\Debug\juce_VST_Wrapper.o build\intermediate\Debug\BinaryData.o build\intermediate\Debug\CabbageCallOutBox.o build\intermediate\Debug\CabbagePluginEditor.o build\intermediate\Debug\CabbageGUIClass.o build\intermediate\Debug\CabbageLookAndFeel.o build\intermediate\Debug\CabbageMainPanel.o build\intermediate\Debug\CabbageTable.o build\intermediate\Debug\csPerfThread.o build\intermediate\Debug\DirectoryContentsComponent.o build\intermediate\Debug\CabbagePropertiesDialog.o build\intermediate\Debug\CodeEditor.o build\intermediate\Debug\ComponentLayoutEditor.o build\intermediate\Debug\CabbagePluginProcessor.o build\intermediate\Debug\Soundfiler.o build\intermediate\Debug\XYPad.o build\intermediate\Debug\XYPadAutomation.o -lgdi32 -luser32 -lkernel32 -lcomctl32 -lcomdlg32 -limm32 -lole32 -loleaut32 -lrpcrt4 -lshlwapi -luuid -lversion-lwininet -lwinmm -lws2_32 -lwsock32 C:\Program_Files_x86\Csound6\bin\csound64.dll  -mwindows cabbage.res

build\intermediate\Debug\juce_PluginUtilities.o: In function `Z24createPluginFilterOfTypeN4juce14AudioProcessor11WrapperTypeE':

D:/cabbage-master/JuceLibraryCode/modules/juce_audio_plugin_client/utility/juce_PluginUtilities.cpp:71: undefined reference to `createPluginFilter()'

build\intermediate\Debug\CabbagePluginEditor.o: In function `ZN33CabbagePluginAudioProcessorEditor15addToRepositoryEN4juce6StringE':

D:/cabbage-master/Source/Plugin/CabbagePluginEditor.cpp:376: undefined reference to `appProperties'

build\intermediate\Debug\CabbagePluginEditor.o: In function `ZN33CabbagePluginAudioProcessorEditor22showInsertControlsMenuEii':

D:/cabbage-master/Source/Plugin/CabbagePluginEditor.cpp:826: undefined reference to `appProperties'

build\intermediate\Debug\CodeEditor.o: In function `ZN16CsoundCodeEditor24codeDocumentTextInsertedERKN4juce6StringEi':

D:/cabbage-master/Source/Editor/CodeEditor.cpp:239: undefined reference to `appProperties'

build\intermediate\Debug\CodeEditor.o: In function `ZN16CsoundCodeEditor17addPopupMenuItemsERN4juce9PopupMenuEPKNS0_10MouseEventE':

D:/cabbage-master/Source/Editor/CodeEditor.cpp:72: undefined reference to `appProperties'

build\intermediate\Debug\CodeEditor.o: In function `ZN16CsoundCodeEditor15addToRepositoryEv':

D:/cabbage-master/Source/Editor/CodeEditor.cpp:144: undefined reference to `appProperties'

build\intermediate\Debug\CodeEditor.o:D:/cabbage-master/Source/Editor/CodeEditor.cpp:149: more undefined references to `appProperties' follow

collect2.exe: error: ld returned 1 exit status