swift234

Stop using getProtocols() in the Clang importer.

The Clang importer was relying on stashing the protocol list within a
nominal type or extension and then retrieving it to fill in all of the
members, which will typically happen before the protocol conformances
can be handled. This prevented the conformance lookup table from being
directly usable for these protocol queries.

In time, the conformance lookup table should have separate callbacks
for "list the protocols to which this conforms" and "provide all of
the conformances", which can make these computations lazier. For now,
use a side table to stash these conformances.

Part of rdar://problem/18448811.

Swift SVN r27980