small speedup in the case where a smallvector is default ctor'd from

an empty vector.  This speeds up llc slightly.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@40983 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/SmallVector.h

@@ -455,6 +455,7 @@ public:
   }
   
   SmallVector(const SmallVector &RHS) : SmallVectorImpl<T>(NumTsAvailable) {
+    if (!RHS.empty())
       operator=(RHS);
   }