Fix Cairo vs. wl_shm pixel formats on big-endian
Weston clients, that use Cairo for drawing, use the Cairo ARGB format. They
translate map this format unconditionally to
WL_SHM_FORMAT_ARGB8888 which is correct on little-endian machines.
That is wrong on big-endian machines. On big-endian machines, the Cairo ARGB format corresponds to
If Weston running on big-endian machine does not support
WL_SHM_FORMAT_BGRA8888, then that support will need to be added.