If neither -a or -i are specified, debhelper commands used to default to acting on...

If neither -a or -i are specified, debhelper commands used to default to acting on all packages in the control file, which was a guaranteed failure if the control file listed packages that did not build for the target architecture. After recent optimisations, this default behavior can efficiently be changed to the more sane default of acting on only packages that can be built for the current architecture. This change is mostly useful when using minimal rules files with dh. Closes: #572077