[config] Enable HB_NO_OT_FONT in HB_NO_OT

CONFIG.md

@@ -90,8 +90,8 @@ without loss of functionality by defining `HB_NO_OT_FONT`.
 
 Most HarfBuzz clients use it for the main shaper, called "ot".  However, it
 is legitimate to want to compile HarfBuzz with only another backend, eg.
-CoreText, for example for an iOS app.  For that, you want `HB_NO_OT_SHAPE`,
-or more generally `HB_NO_OT`.
+CoreText, for example for an iOS app.  For that, you want `HB_NO_OT_SHAPE`.
+If you are going down that route, check if you want `HB_NO_OT`.
 
 This is very rarely what you need.  Make sure you understand exactly what you
 are doing.

src/hb-config.hh

@@ -122,6 +122,7 @@
 #endif
 
 #ifdef HB_NO_OT
+#define HB_NO_OT_FONT
 #define HB_NO_OT_SHAPE
 #endif