swift234

Turn on the materializeForSet-in-protocol-extensions fix from
r31072 (<rdar://21836671>).

Passes the primary test suite; I'm still working on giving it
proper tests, but since time is of the essence, we can
streamline this process by doing a few things in parallel.

The test suite change here is interesting: we're no longer
emitting materializeForSet entrypoints for storage in
protocol extensions, because they were only getting emitted
lazily and we're no longer using them at all.  I think
that's fine because, well, we're no longer using them at
all.

Swift SVN r31192