Update SetVector to rely on the underlying set's insert to return a pair<iterator, bool>

This is to be consistent with StringSet and ultimately with the standard
library's associative container insert function.

This lead to updating SmallSet::insert to return pair<iterator, bool>,
and then to update SmallPtrSet::insert to return pair<iterator, bool>,
and then to update all the existing users of those functions...

llvm-svn: 222334
diff --git a/llvm/lib/Transforms/ObjCARC/DependencyAnalysis.cpp b/llvm/lib/Transforms/ObjCARC/DependencyAnalysis.cpp
index 5429098..f6c236c 100644
--- a/llvm/lib/Transforms/ObjCARC/DependencyAnalysis.cpp
+++ b/llvm/lib/Transforms/ObjCARC/DependencyAnalysis.cpp
@@ -229,7 +229,7 @@
           // Add the predecessors to the worklist.
           do {
             BasicBlock *PredBB = *PI;
-            if (Visited.insert(PredBB))
+            if (Visited.insert(PredBB).second)
               Worklist.push_back(std::make_pair(PredBB, PredBB->end()));
           } while (++PI != PE);
         break;