plugin: Add a --verbose command line option

And only output the version information if that is specified. It’s too
loud otherwise.
scripts: Handle running under ./configure

If
    scan-build --use-analyzer=/path/to/tartan ./configure
is run, the $first_arg is ‘--version’, not ‘-cc1’. Gracefully handle
that by not printing a warning, and instead printing some version
information.
bugs: Update the file descriptor bug with an ML link