[ignition] Fix -Wsign-compare warnings.

src/interpreter/bytecode-register-optimizer.h

Index: src/interpreter/bytecode-register-optimizer.h
diff --git a/src/interpreter/bytecode-register-optimizer.h b/src/interpreter/bytecode-register-optimizer.h
index 885f10f3441e9159c5a6a24063d0de5480adfdcb..e2a02cf5948595391c338555430b40240df024ff 100644
--- a/src/interpreter/bytecode-register-optimizer.h
+++ b/src/interpreter/bytecode-register-optimizer.h
@@ -137,7 +137,8 @@ class V8_EXPORT_PRIVATE BytecodeRegisterOptimizer final
 
   uint32_t NextEquivalenceId() {
     equivalence_id_++;
-    CHECK_NE(equivalence_id_, kInvalidEquivalenceId);
+    // TODO(rmcilroy): use the same type for these and remove static_cast.
+    CHECK_NE(static_cast<size_t>(equivalence_id_), kInvalidEquivalenceId);
     return equivalence_id_;
   }