Fix to 32-bit kernel.

runtime/vm/kernel_binary_flowgraph.cc

Index: runtime/vm/kernel_binary_flowgraph.cc
diff --git a/runtime/vm/kernel_binary_flowgraph.cc b/runtime/vm/kernel_binary_flowgraph.cc
index adcfcec719e3b803ee48ddef5a1239653079e14e..33c85883c08dca768e4f896411db799a63c561f3 100644
--- a/runtime/vm/kernel_binary_flowgraph.cc
+++ b/runtime/vm/kernel_binary_flowgraph.cc
@@ -3495,7 +3495,9 @@ Fragment StreamingFlowGraphBuilder::BuildGetMainClosure() {
           Function::Handle(Z, function.ImplicitClosureFunction());
       const Instance& closure =
           Instance::ZoneHandle(Z, closure_function.ImplicitStaticClosure());
-      return Constant(closure) + Return(TokenPosition::kNoSource);
+      Fragment instructions = Constant(closure);
+      instructions += Return(TokenPosition::kNoSource);
+      return instructions;
     } else {
       UNIMPLEMENTED();
     }