Add wxUSE_PRIVATE_FONTS and drop wxHAS_PRIVATE_FONTS

Handle this feature as all the other ones and provide a configure switch
and a setup.h option to disable it if necessary, as it may be desirable
to do it, especially under Linux, to avoid extra dependency on pangoft2
if this functionality is unnecessary.

include/wx/setup_inc.h

@@ -1138,6 +1138,16 @@
 // Recommended setting: 1 (but can be safely disabled if you don't use it)
 #define wxUSE_PREFERENCES_EDITOR 1
 
+// wxFont::AddPrivateFont() allows to use fonts not installed on the system by
+// loading them from font files during run-time.
+//
+// Default is 1 except under Unix where it will be turned off by configure if
+// the required libraries are not available or not new enough.
+//
+// Recommended setting: 1 (but can be safely disabled if you don't use it and
+// want to avoid extra dependencies under Linux, for example).
+#define wxUSE_PRIVATE_FONTS 1
+
 // wxRichToolTip is a customizable tooltip class which has more functionality
 // than the stock (but native, unlike this class) wxToolTip.
 //