Don't use any default unicode funcs if HB_NO_UNICODE_FUNCS is defined

Part of https://github.com/harfbuzz/harfbuzz/issues/1652

src/hb-unicode.cc

@@ -130,11 +130,11 @@ extern "C" hb_unicode_funcs_t *hb_ucdn_get_unicode_funcs ();
 hb_unicode_funcs_t *
 hb_unicode_funcs_get_default ()
 {
-#if defined(HAVE_UCDN)
+#if !defined(HB_NO_UNICODE_FUNCS) && defined(HAVE_UCDN)
   return hb_ucdn_get_unicode_funcs ();
-#elif defined(HAVE_GLIB)
+#elif !defined(HB_NO_UNICODE_FUNCS) && defined(HAVE_GLIB)
   return hb_glib_get_unicode_funcs ();
-#elif defined(HAVE_ICU) && defined(HAVE_ICU_BUILTIN)
+#elif !defined(HB_NO_UNICODE_FUNCS) && defined(HAVE_ICU) && defined(HAVE_ICU_BUILTIN)
   return hb_icu_get_unicode_funcs ();
 #else
 #define HB_UNICODE_FUNCS_NIL 1