fix: move unique_ptr<T> to be converted to llvm::Expected

gcc 6.3 was complaining about not being able to wrap it in an
llvm::Expected

compiler/lib/Support/KeySet.cpp

@@ -48,7 +48,7 @@ KeySet::generate(ClientParameters &params, uint64_t seed_msb,
            << "Cannot setup encryption material: " << std::move(fillError);
   }
 
-  return a;
+  return std::move(a);
 }
 
 std::unique_ptr<KeySet> KeySet::uninitialized() {