Ship UCDN and use it by default

So we are not relying on version of Unicode data in glib...

Fixes https://github.com/behdad/harfbuzz/issues/386
Fixes https://github.com/behdad/harfbuzz/issues/388

src/hb-unicode.cc

diff --git a/src/hb-unicode.cc b/src/hb-unicode.cc
index 487d10b..d553a71 100644
--- a/src/hb-unicode.cc
+++ b/src/hb-unicode.cc
@@ -131,12 +131,12 @@
 #define HB_UNICODE_FUNCS_IMPLEMENT(set) \
   return hb_##set##_get_unicode_funcs ();
 
-#ifdef HAVE_GLIB
+#if defined(HAVE_UCDN)
+  HB_UNICODE_FUNCS_IMPLEMENT(ucdn)
+#elif defined(HAVE_GLIB)
   HB_UNICODE_FUNCS_IMPLEMENT(glib)
 #elif defined(HAVE_ICU) && defined(HAVE_ICU_BUILTIN)
   HB_UNICODE_FUNCS_IMPLEMENT(icu)
-#elif defined(HAVE_UCDN)
-  HB_UNICODE_FUNCS_IMPLEMENT(ucdn)
 #else
 #define HB_UNICODE_FUNCS_NIL 1
   HB_UNICODE_FUNCS_IMPLEMENT(nil)