Change file permissions for some setuid executables so they are "o+r".
The executable itself doesn't contain any privileged information.

An example of where this is useful is when makefs(8) is creating an image
that includes /sbin/shutdown. This can now be done without root privileges.

Reviewed by: delphij
Discussed with: delphij, des
CR: https://reviews.freebsd.org/D662