The timestamp-based rules of make do not work well for the publish tool
because depot archives are often re-created with the same content but a
different modification time, in particular when creating archives via
'FORCE'. This way, those archives are re-published every time, which
becomes a time-consuming operation since all archives must be signed.
This patch filters the targets based on the content that is already
present in the public/ location. All existing archives are skipped.
7670f048c1