- Support completing dynamic make targets.
- Support completing make targets when using -C/--directory.

- Remove the unnecessary echo.
- Support `-Cdir/path`, `-C dir/path`
- Support `--directory=dir/path`, `--directory dir/path`

Since we filter by text that is localized we need to ensure the correct
locale is used.

This detects if the make command have the `-p` switch otherwise it
assumes it is BSD make and will run a different command to try to figure
out the available targets.

Suppress the output both to stdout and stderr in the check for the
option. Also provide the directory (`C`) instead of utilizing an empty
Makefile.

It seems the empty Makefile (`/dev/null`) returns status code 1 which
fails the check and means that it will always be assumed to be FreeBSD.

We don't want to run the default make target when testing for the command.