hwclock: allow -l as alias for --localtime

hwclock: allow -l as alias for --localtime

For symmetry with --utc where a short form is already allowed, and to
make it easier to write scripts that will work with both util-linux'
and busybox' hwclock, make -l another spelling of
--localtime. (Busybox also understands --localtime, but only if it has
been compiled with long option support.)