Support for run-time loading of compiler plugins.
Add plugin phases to phase plan
Load all available plugins. Skips plugins that either have the same name as another one, or which define a phase name that another one does.
Load a rough list of the plugins. For speed, it does not instantiate a compiler run. Therefore it cannot test for same-named phases or other problems that are filtered from the final list of plugins.
A description of all the plugins that are loaded
Summary of the options for all loaded plugins