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/TwoAddressInstructionPass.cpp b/llvm/lib/CodeGen/TwoAddressInstructionPass.cpp
index 428846a..e218a83 100644
--- a/llvm/lib/CodeGen/TwoAddressInstructionPass.cpp
+++ b/llvm/lib/CodeGen/TwoAddressInstructionPass.cpp
@@ -678,7 +678,7 @@
   unsigned Reg = DstReg;
   while (MachineInstr *UseMI = findOnlyInterestingUse(Reg, MBB, MRI, TII,IsCopy,
                                                       NewReg, IsDstPhys)) {
-    if (IsCopy && !Processed.insert(UseMI))
+    if (IsCopy && !Processed.insert(UseMI).second)
       break;
 
     DenseMap<MachineInstr*, unsigned>::iterator DI = DistanceMap.find(UseMI);