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...

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222334 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/SCCP.cpp

@@ -214,7 +214,8 @@ public:
   ///
   /// This returns true if the block was not considered live before.
   bool MarkBlockExecutable(BasicBlock *BB) {
-    if (!BBExecutable.insert(BB)) return false;
+    if (!BBExecutable.insert(BB).second)
+      return false;
     DEBUG(dbgs() << "Marking Block Executable: " << BB->getName() << '\n');
     BBWorkList.push_back(BB);  // Add the block to the work list!
     return true;