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/Utils/LoopUnroll.cpp b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
index 7b06645..0e1baa1 100644
--- a/llvm/lib/Transforms/Utils/LoopUnroll.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
@@ -112,7 +112,7 @@
   if (LPM) {
     if (ScalarEvolution *SE = LPM->getAnalysisIfAvailable<ScalarEvolution>()) {
       if (Loop *L = LI->getLoopFor(BB)) {
-        if (ForgottenLoops.insert(L))
+        if (ForgottenLoops.insert(L).second)
           SE->forgetLoop(L);
       }
     }