swift234

Fix a use-after-free caused by creating DerivedFileUnit on the fly

Sema was creating DerivedFileUnit on the fly, while something else is iterating
over FileUnits in the module.  The fix is to create DerivedFileUnit in advance.
This change immediately uncovered a lot of code that assumed that the module
consists of a single FileUnit at certain conditions.  This patch also fixes
that code (SourceKit patch is separate, not sending it).

The test change is because now operator == on NSObjects is correctly recognised
as coming from a system module.

rdar://16153700, rdar://16227621, possibly rdar://16049613


Swift SVN r14692