lorder: Clean up and improve robustness.

• Properly parse (no) command-line options.

• Ensure that errors go to stderr and result in a non-zero exit.

• Drop the special-case code for a single argument, as it will produce the wrong outcome if the file does not exist or is corrupted.

• Don't print anything until after we've collected all the data.

• Always create all temporary files before setting the trap. This ensures that the trap can safely fire at any moment, regardless of any previous definition of T.

• Use a temporary file rather than a pipe between nm and sed to ensure proper termination if nm fails due to a missing or invalid input.

• The check for self-referential entries was conditional on testing our argument list against a regex looking for archives. This was a needless and unreliable optimization; make the check unconditional.

• Document that lorder will not work properly if any of its inputs have spaces in their name.

MFC after: 1 week
Sponsored by: Klara, Inc.
Reviewed by: allanjude
Differential Revision: https://reviews.freebsd.org/D44133