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/RegAllocFast.cpp b/llvm/lib/CodeGen/RegAllocFast.cpp
index 1bfd93b..8fc10b4 100644
--- a/llvm/lib/CodeGen/RegAllocFast.cpp
+++ b/llvm/lib/CodeGen/RegAllocFast.cpp
@@ -708,7 +708,7 @@
       continue;
     if (MO.isEarlyClobber() || MI->isRegTiedToDefOperand(i) ||
         (MO.getSubReg() && MI->readsVirtualRegister(Reg))) {
-      if (ThroughRegs.insert(Reg))
+      if (ThroughRegs.insert(Reg).second)
         DEBUG(dbgs() << ' ' << PrintReg(Reg));
     }
   }