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

include/swift/AST/Module.h

@@ -26,6 +26,7 @@
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/SmallSet.h"
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/TinyPtrVector.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -42,6 +43,7 @@ namespace swift {
   enum class DeclKind : uint8_t;
   class ExtensionDecl;
   class DebuggerClient;
+  class DerivedFileUnit;
   class FileUnit;
   class FuncDecl;
   class InfixOperatorDecl;
@@ -172,7 +174,7 @@ private:
   // FIXME: Do we really need to bloat all modules with this?
   DebuggerClient *DebugClient = nullptr;
 
-  TinyPtrVector<FileUnit *> Files;
+  SmallVector<FileUnit *, 2> Files;
 
   Module(Identifier name, ASTContext &ctx);
 public:
@@ -198,6 +200,8 @@ public:
   /// dealing with.
   FileUnit &getMainFile(FileUnitKind expectedKind) const;
 
+  DerivedFileUnit &getDerivedFileUnit() const;
+
   DebuggerClient *getDebugClient() const { return DebugClient; }
   void setDebugClient(DebuggerClient *R) {
     assert(!DebugClient && "Debugger client already set");
@@ -555,13 +559,16 @@ public:
 /// A container for a module-level definition derived as part of an implicit
 /// protocol conformance.
 class DerivedFileUnit final : public FileUnit {
-  FuncDecl *const DerivedDecl;
-  
+  TinyPtrVector<FuncDecl *> DerivedDecls;
+
 public:
-  DerivedFileUnit(Module &M, FuncDecl *derivedDecl)
-    : FileUnit(FileUnitKind::Derived, M), DerivedDecl(derivedDecl) {}
-  ~DerivedFileUnit() {}
-  
+  DerivedFileUnit(Module &M);
+  ~DerivedFileUnit() = default;
+
+  void addDerivedDecl(FuncDecl *FD) {
+    DerivedDecls.push_back(FD);
+  }
+
   void lookupValue(Module::AccessPathTy accessPath, Identifier name,
                    NLKind lookupKind,
                    SmallVectorImpl<ValueDecl*> &result) const override;