Describe the bug

webpack --flag --help shows inconsistent behavior, sometimes it prints help sometimes it considers --help as value for --flag.

What is the current behavior?

To Reproduce

Steps to reproduce the behavior:

Try running -

webpack --stats --help
webpack --mode --help
webpack -hot --help
webpack --entry --help

See inconsistency.

Expected behavior
The behavior should be consistent either print help (recommended) or throw an error/warning.

Screenshots

Please paste the results of webpack-cli info here, and mention other relevant information

Additional context
webpack/webpack.js.org#4051 (comment)