util-linux: Add fcntl-lock

util-linux: Add fcntl-lock

Add a version of flock that uses the fnctl based lockf locking instead of
flock based locks. This allows us to take the same lock that opkg would
use from a shell script. The two different locking mechanisms operate
independently of each other.

Inserting this C file into the util-linux build seems like the easiest/best
place to insert the code. At this point it hasn't been discussed with upstream.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>