Add return that was lost somehow in my last commit.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217810 91177308-0d34-0410-b5e6-96231b3b80d8

lib/ExecutionEngine/Interpreter/Interpreter.h

@@ -45,6 +45,7 @@ public:
   AllocaHolder(AllocaHolder &&RHS) : Allocations(std::move(RHS.Allocations)) {}
   AllocaHolder &operator=(AllocaHolder &&RHS) {
     Allocations = std::move(RHS.Allocations);
+    return *this;
   }
 
   ~AllocaHolder() {