MiscGui.cpp:1434:18: error: 'fl_display' was not declared ...

Other files are using x.H, but that header is deprecated and
the correct one is platform.H. fl_display is X-specific, so
this likely cannot work without fltk[X] at the moment.
--- a/UI/MiscGui.cpp
+++ b/UI/MiscGui.cpp
@@ -28,6 +28,7 @@
 
 #include <FL/Fl.H>
 #include <FL/fl_draw.H>
+#include <FL/platform.H>
 
 #include <cairo.h>
 #include <cairo-xlib.h>