WORD64 seems to have only been defined in <X11/Xmd.h> when building for
CRAY, to handle int being a 64-bit value (ILP64, not LP64) and having
64-bit alignment requirements.

It hadn't been fully supported even before autotooling, as can be
seen by removed code such as:

 #ifdef WORD64
 _XkbWriteCopyData32 Not Implemented Yet for sizeof(int)==8
 #endif

(mostly performed with unifdef, followed by some manual cleanup of
 the remaining code)

Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>