1.0.23.40: export page sizes to C with LU suffix

1.0.23.40: export page sizes to C with LU suffix

 * Rename GENCGC-PAGE-SIZE and *BACKEND-PAGE-SIZE* to
   GENCGC-PAGE-BYTES and *BACKEND-PAGE-BYTES* respectively.

 * Clean up constant.h generation: instead of guessing when to add an
   U suffix, specify when the value is "large", and then add an LU
   suffix.

 * Without the LU suffix some C compilers chose to truncate results of
   some operations where these quantities featured, leading at least
   to an upper limit of #xffff0000 bytes in dynamic space on certain
   64 bit systems.