sort-with-subports.tcl should print all ports that need to be built

[ryandesign (Ryan Carsten Schmidt)]

Currently sort-with-subports.tcl, which is used by mpbb-list-subports, traverses the entire dependency tree of the given port and all of its subports, and it prints the names of those ports that have not yet been built and uploaded, limited to the given port and its subports. That limit should be removed: it should print the names of all ports in the dependency tree that need to be built.

The name mpbb-list-subports will then become inaccurate; mpbb-list-ports would be better.

This change will improve the buildbot so that each port that needs to be built will happen in its own build—a build that can be referred to by URL later, a build that can report its status to the web app.

Once this is done we can simplify mpbb-gather-archives so that it only gathers archives for the given port, since the dependencies' archives will already have been gathered by their separate builds.

[jmroot (Joshua Root)]

This would need to query the failcache in order to avoid repeatedly building dependencies that are failing.

[jmroot (Joshua Root)]

In bb4a1f6089ee09fc20d00d3556311c3b0e7d2d99/mpbb (master):

mpbb: preprocessing improvements

• Start separate builds for unbuilt dependencies.
• gather-archives can therefore consider only the port being built and not worry about its deps.
• Exclude ports that have any dependency that sets 'known_fail yes'.
• Exclude dependencies that have a failcache entry or have a recursive dependency that does. The ports that the build was actually requested for are still built even if a dep is in the failcache, so that the failure will be reported to maintainers.
• Delete stale entries from the failcache for relevant ports while we're at it.

Fixes: #60935