Summary:
For `PhutilSymbolLoader` queries which include `setAncestorClass()`, we need the map of which classes/interfaces things extend/implement to issue the query efficiently.
Without this map, we need to load //every// class/interface and then do `is_subclass_of()`. This is doable, but not very performant if we don't have php-fpm warmup. There are a few performance-sensitive interfaces where we run queries like this, including some in Arcanist, where we'll never have warmup.
This map isn't particularly difficult to generate or maintain, so just include it in symbol generation and in the library map.
Also set parallelism with a flag, since it was arbitrarily hard-coded and adding flags is easy. 8 actually seems approximately optimal on my machine at least, though.
Test Plan: Ran "phutil_rebuild_map.php", opened library map, got a reasonable extension map.
Reviewers: vrana, btrahan
Reviewed By: vrana
CC: aran
Maniphest Tasks: T1103
Differential Revision: https://secure.phabricator.com/D2585