add "const" attribute, where possible

add "const" attribute, where possible

* maint.mk (sc_const_long_option): New rule.  Enforce global change.
* src/base64.c (long_options): Use "const" where possible.
* src/cat.c (main): Likewise.
* src/chcon.c (long_options): Likewise.
* src/chgrp.c (long_options): Likewise.
* src/chmod.c (long_options): Likewise.
* src/chown.c (long_options): Likewise.
* src/comm.c (long_options, OUTPUT_DELIMITER_OPTION): Likewise.
* src/cp.c (long_opts): Likewise.
* src/csplit.c (longopts): Likewise.
* src/cut.c (longopts): Likewise.
* src/date.c (long_options): Likewise.
* src/dd.c (conversions, flags, statuses): Likewise.
* src/df.c (long_options): Likewise.
* src/dircolors.c (long_options): Likewise.
* src/du.c (long_options): Likewise.
* src/env.c (longopts): Likewise.
* src/expand.c (longopts): Likewise.
* src/fmt.c (long_options): Likewise.
* src/fold.c (longopts): Likewise.
* src/groups.c (longopts): Likewise.
* src/head.c (long_options): Likewise.
* src/id.c (longopts): Likewise.
* src/install.c (long_options): Likewise.
* src/join.c (longopts): Likewise.
* src/kill.c (long_options): Likewise.
* src/ln.c (long_options): Likewise.
* src/ls.c (long_time_format, long_options, sort_functions): Likewise.
* src/md5sum.c (long_options): Likewise.
* src/mkdir.c (longopts): Likewise.
* src/mkfifo.c (longopts): Likewise.
* src/mknod.c (longopts): Likewise.
* src/mktemp.c (longopts): Likewise.
* src/mv.c (long_options): Likewise.
* src/nice.c (longopts): Likewise.
* src/nl.c (longopts): Likewise.
* src/od.c (charname, long_options): Likewise.
* src/paste.c (longopts): Likewise.
* src/pathchk.c (longopts): Likewise.
* src/pinky.c (longopts): Likewise.
* src/pr.c (long_options): Likewise.
* src/ptx.c (long_options): Likewise.
* src/readlink.c (longopts): Likewise.
* src/rm.c (long_opts): Likewise.
* src/rmdir.c (longopts): Likewise.
* src/runcon.c (long_options): Likewise.
* src/seq.c (long_options): Likewise.
* src/shred.c (long_opts): Likewise.
* src/shuf.c (long_opts): Likewise.
* src/sort.c (monthtab, long_options): Likewise.
* src/split.c (longopts): Likewise.
* src/stat.c (long_options): Likewise.
* src/stty.c (mode_info, control_info, longopts, set_mode) Likewise.
(set_control_char, speeds): Likewise.
* src/su.c (longopts): Likewise.
* src/sum.c (longopts): Likewise.
* src/tac.c (longopts): Likewise.
* src/tail.c (long_options): Likewise.
* src/tee.c (long_options): Likewise.
* src/timeout.c (long_options): Likewise.
* src/touch.c (longopts): Likewise.
* src/tr.c (long_options): Likewise.
* src/truncate.c (longopts): Likewise.
* src/tty.c (longopts): Likewise.
* src/uname.c (uname_long_options, arch_long_options): Likewise.
* src/unexpand.c (longopts): Likewise.
* src/uniq.c (longopts): Likewise.
* src/wc.c (longopts): Likewise.
* src/who.c (longopts): Likewise.