Add a way to preserve stdio  #minor
Add a way to preserve stdio  #minor

This change makes it possible to use stdio across the compiler. It's
only enabled with --disable-sandboxing, because that might leak a file
descriptor that was open outside of the container, defeating the whole
purpose.

omegaup/omegajail,omegaup/omegajail,omegaup/omegajail,omegaup/omegajail,omegaup/omegajail,omegaup/omegajail,omegaup/omegajail,omegaup/omegajail,omegaup/omegajail,omegaup/omegajail,omegaup/omegajail