Get rid of the confusing old USING_WIN_UI define. Make a more clear system property for headless.

ext/native/tools/atlastool.cpp

@@ -42,7 +42,9 @@
 #include "Common/CommonTypes.h"
 #include "Common/Data/Format/ZIMSave.h"
 #include "kanjifilter.h"
+#include "Common/System/System.h"
 
+bool System_GetPropertyBool(SystemProperty prop) { return false; }
 
 constexpr int supersample = 16;
 constexpr int distmult = 64 * 3;  // this is "one pixel in the final version equals 64 difference". reduce this number to increase the "blur" radius, increase it to make things "sharper"

ext/native/tools/zimtool.cpp

@@ -5,10 +5,13 @@
 #include "Common/Data/Format/PNGLoad.h"
 #include "Common/Data/Format/ZIMLoad.h"
 #include "Common/Data/Format/ZIMSave.h"
-
+#include "Common/System/System.h"
 #include "Common/Common.h"
 
-char magic[5] = "ZIMG";
+
+bool System_GetPropertyBool(SystemProperty prop) { return false; }
+
+static const char magic[5] = "ZIMG";
 
 const char *format_strings[4] = { "8888", "4444", "565", "ETC1" };
 int formats[3] = { ZIM_RGBA8888, ZIM_RGBA4444, ZIM_RGB565 };