The --tool-opt runner option is the recommended practice for allowing
runners to take additional arguments that are passed on to the
underlying tool. It exists because we don't want to add one runner
option for every single tool option that users might want to tweak --
that would be a nightmare.
Enough runners are using this option that it's time to promote it to a
common runner capability with consistent behavior, the same way we did
for the --dev-id option in the past. This removes boilerplate from
individual runner files and ensures consistent argument handling for
this option when it is supported.
Since --tool-opt is a bit long to type, and we've had some complaints
about that, take this as an opportunity to standardize on -O as a
short option equivalent for it.
Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>