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/MachineSink.cpp b/llvm/lib/CodeGen/MachineSink.cpp
index b82d4e6..ba25bca 100644
--- a/llvm/lib/CodeGen/MachineSink.cpp
+++ b/llvm/lib/CodeGen/MachineSink.cpp
@@ -340,7 +340,7 @@
   // If the pass has already considered breaking this edge (during this pass
   // through the function), then let's go ahead and break it. This means
   // sinking multiple "cheap" instructions into the same block.
-  if (!CEBCandidates.insert(std::make_pair(From, To)))
+  if (!CEBCandidates.insert(std::make_pair(From, To)).second)
     return true;
 
   if (!MI->isCopy() && !TII->isAsCheapAsAMove(MI))