Headless build

[d.healey]

Trying to do a headless build but getting a lot of these messages. @Christoph-Hart Any ideas?

                 from ../../JuceLibraryCode/include_juce_audio_plugin_client_VST2.cpp:9:
/media/dave/Work 1/HISE Development Builds/HISE/JUCE/modules/juce_audio_plugin_client/VST/juce_VST_Wrapper.cpp: In member function ‘virtual void SharedMessageThread::run()’:
/media/dave/Work 1/HISE Development Builds/HISE/JUCE/modules/juce_audio_plugin_client/VST/juce_VST_Wrapper.cpp:231:9: error: ‘ScopedXDisplay’ was not declared in this scope
         ScopedXDisplay xDisplay;
         ^~~~~~~~~~~~~~
/media/dave/Work 1/HISE Development Builds/HISE/JUCE/modules/juce_audio_plugin_client/VST/juce_VST_Wrapper.cpp:231:9: note: suggested alternative: ‘XOpenDisplay’
         ScopedXDisplay xDisplay;
         ^~~~~~~~~~~~~~
         XOpenDisplay
In file included from /media/dave/Work 1/HISE Development Builds/HISE/JUCE/modules/juce_audio_plugin_client/juce_audio_plugin_client_VST2.cpp:27:0,