--diagnosticAsError: Must be followed by a comma-separated list of non-fatal-error PPxxxx diagnostic codes that should get turned into (recoverable) errors.
--noDiagnostic: Must be followed by a comma-separated list of non-fatal-error PPxxxx diagnostic codes that should get suppressed.
Release notes: Adding CLI options --warnaserror, --diagnosticaserror, --nodiagnostic
This resolves #2517.
Adding tests.