Fail compile if no shapers enabled

src/hb-shaper.cc

@@ -34,6 +34,7 @@ static const hb_shaper_entry_t all_shapers[] = {
 #include "hb-shaper-list.hh"
 #undef HB_SHAPER_IMPLEMENT
 };
+static_assert (0 != ARRAY_LENGTH_CONST (all_shapers), "No shaper enabled.");
 
 #if HB_USE_ATEXIT
 static void free_static_shapers ();