With the new solver, we're only about 30% slower than the old type
checker when parsing swift.swift. That's close enough to stop using it
as an excuse to keep the old type checker around. Overall "lit" times
are about the same as before we switched to the new solver.
Swift SVN r5284
This replaces the obscure, inefficient lookup into extensions with
something more straightforward: walk all of the known extensions
(available as a simple list), then eliminate any declarations that
have been shadowed by other declarations. The shadowing rules still
need to consider the module re-export DAG, but we'll leave that for
later.
As part of this, keep track of the last time we loaded extensions for
a given nominal type. If the list of extensions is out-of-date with
respect to the global generation count (which tracks resolved module
imports), ask the modules to load any additional extensions. Only the
Clang module importer can currently load extensions in this manner.
Swift SVN r5223
This paves the way for having a Swift module importer. The eventual goal
here is to eliminate all explicit uses of the Clang module loader, but
I'm not going to push too hard on that for now.
Swift SVN r5092
