This can be useful for setting some meson global options, such as the
optimization level or debug state.xs

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20230801130403.164060-7-berrange@redhat.com>
[thuth: Move the help text into the section with the other --... options]
Signed-off-by: Thomas Huth <thuth@redhat.com>