[gvar] Add memory-barrier as in ArrayOf

src/hb-ot-var-gvar-table.hh

@@ -501,6 +501,7 @@ struct gvar
   unsigned get_offset (unsigned i) const
   {
     if (unlikely (i > glyphCount)) return 0;
+    _hb_compiler_memory_r_barrier ();
     return is_long_offset () ? get_long_offset_array ()[i] : get_short_offset_array ()[i] * 2;
   }