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/Scalar/ScalarReplAggregates.cpp b/llvm/lib/Transforms/Scalar/ScalarReplAggregates.cpp
index c6d6ec7..f7fa917 100644
--- a/llvm/lib/Transforms/Scalar/ScalarReplAggregates.cpp
+++ b/llvm/lib/Transforms/Scalar/ScalarReplAggregates.cpp
@@ -1669,7 +1669,7 @@
                                            AllocaInfo &Info) {
   // If we've already checked this PHI, don't do it again.
   if (PHINode *PN = dyn_cast<PHINode>(I))
-    if (!Info.CheckedPHIs.insert(PN))
+    if (!Info.CheckedPHIs.insert(PN).second)
       return;
 
   for (User *U : I->users()) {