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/Analysis/CaptureTracking.cpp b/llvm/lib/Analysis/CaptureTracking.cpp
index f2f8877..a271729 100644
--- a/llvm/lib/Analysis/CaptureTracking.cpp
+++ b/llvm/lib/Analysis/CaptureTracking.cpp
@@ -239,7 +239,7 @@
         if (Count++ >= Threshold)
           return Tracker->tooManyUses();
 
-        if (Visited.insert(&UU))
+        if (Visited.insert(&UU).second)
           if (Tracker->shouldExplore(&UU))
             Worklist.push_back(&UU);
       }