dont put MAXMCLBYTES in the mclsizes array with a comment saying its 64k when the macro can change without automatically fixing the comment.
dont put MAXMCLBYTES in the mclsizes array with a comment saying its 64k
when the macro can change without automatically fixing the comment.

instead add a diagnostic that checks that the biggest cluster size is
always MAXMCLBYTES.

requested by and ok kettenis@

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars