[turbofan] Do not reduce Return nodes with multiple value inputs.

src/compiler/common-operator.h

Index: src/compiler/common-operator.h
diff --git a/src/compiler/common-operator.h b/src/compiler/common-operator.h
index dd33188e1c35c79be00d4f3b5e2853fba79710f3..5d0a6df31da115b088776bc4e6be4fd4d18a5f35 100644
--- a/src/compiler/common-operator.h
+++ b/src/compiler/common-operator.h
@@ -49,6 +49,9 @@ V8_EXPORT_PRIVATE BranchHint BranchHintOf(const Operator* const);
 // Deoptimize reason for Deoptimize, DeoptimizeIf and DeoptimizeUnless.
 DeoptimizeReason DeoptimizeReasonOf(Operator const* const);
 
+// Helper function for return nodes, because returns have a hidden value input.
+int ValueInputCountOfReturn(Operator const* const op);
+
 // Deoptimize bailout kind.
 enum class DeoptimizeKind : uint8_t { kEager, kSoft };