LU-4924 - chmod g+s, touch should not clear sgid bit
$ mkdir 4924
$ cd 4924
$ touch f
$ chmod u=rwx,g=rwxs f
$ ls -l f | awk -- '{sub(/\\./, "", $1); print $1, $3, $4 }'
> -rwxrwsr-- root root
$ touch f
$ ls -l f | awk -- '{sub(/\\./, "", $1); print $1, $3, $4 }'
> -rwxrwsr-- root root
$ cd ..
$ rm -rf 4924