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/CodeGen/MachineBlockPlacement.cpp b/llvm/lib/CodeGen/MachineBlockPlacement.cpp
index 661a4e3..08fd200 100644
--- a/llvm/lib/CodeGen/MachineBlockPlacement.cpp
+++ b/llvm/lib/CodeGen/MachineBlockPlacement.cpp
@@ -813,7 +813,7 @@
                                    BE = L.block_end();
        BI != BE; ++BI) {
     BlockChain &Chain = *BlockToChain[*BI];
-    if (!UpdatedPreds.insert(&Chain))
+    if (!UpdatedPreds.insert(&Chain).second)
       continue;
 
     assert(Chain.LoopPredecessors == 0);
@@ -914,7 +914,7 @@
   for (MachineFunction::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) {
     MachineBasicBlock *BB = &*FI;
     BlockChain &Chain = *BlockToChain[BB];
-    if (!UpdatedPreds.insert(&Chain))
+    if (!UpdatedPreds.insert(&Chain).second)
       continue;
 
     assert(Chain.LoopPredecessors == 0);