Codechange: Refactor the Freetype font cache into a generic part that does not depend on Freetype and into one that does.

This makes it easier to add other TrueType font rendering engines.

src/settings.cpp

@@ -68,6 +68,10 @@
 #include "void_map.h"
 #include "station_base.h"
 
+#if defined(WITH_FREETYPE)
+#define HAS_TRUETYPE_FONT
+#endif
+
 #include "table/strings.h"
 #include "table/settings.h"