In file included from gfx/thebes/Unified_cpp_gfx_thebes1.cpp:11:
gfx/thebes/gfxHarfBuzzShaper.cpp:1571:41: error: use of
  undeclared identifier 'HB_BUFFER_CLUSTER_LEVEL_MONOTONE_CHARACTERS'
  hb_buffer_set_cluster_level(buffer, HB_BUFFER_CLUSTER_LEVEL_MONOTONE_CHARACTERS);
  ^