Option to fail on warnings

I would like to propose an option that could make the compiler fail if at least one warning is encountered, regardless of errors and exit with a non-zero exit code.

This could be a simple flags such as `--fail-on-warnings` or a more sophisticated setting like `--error-level` that could introduce more granular control, i.e. still exit with 0 if compilation failed with errors.

Use case for this is either a purist approach when no warnings are tolerated or code quality control CI job that verifies new code with `--checks-only`.