With NS3.3 (m68k), sudo-1.6.3p7 compiles cleanly. sudo works, but visudo always
complains about the sudoers file being already locked.

Reason:
sudo finds and uses lockf(), but for some reason the lockf() call in lock_file()
always return -1, errno=EINVAL for my system (note that EINVAL isn't even a
documented return for my lockf(), and that AFAIK lockf() is generally working on
NS.)

Workaround:
Use flock() instead of lockf() by enabling HAVE_FLOCK instead of HAVE_LOCKF in
config.h. (I haven't tried to automate this with configure, so at least a notice
in the docs seems useful.)
The appended patch also includes the header file for flock() and fixes a
possible typo for SUDO_UNLOCK. (This seems to also affect sudo with logging to
file and flock() locking.)