how to remove that hardcoded legacy modifier masks like XKB_COMMON_SHIFT_MASK

[Juan Zhao]

  Hi Daniel,
     I saw your patch in xkbcommom: 
http://cgit.freedesktop.org/xorg/lib/libxkbcommon/commit/?id=3dcd7ae02ccfd47b2a9a552daa225255803e66cf
     It deletes the macros like XKB_COMMON_SHIFT_MASK. You suggest to 
use the xkb_state_mod_* and xkb_map_mod_* API instead.
     Would Weston also use this method to update, looks like 
weston-clients can not build against to the tip code of libxkbcommon?

Thanks,
Juan