[ignition] Fix -Wsign-compare warnings.

src/interpreter/bytecode-register-optimizer.h

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_INTERPRETER_BYTECODE_REGISTER_OPTIMIZER_H_
 #define V8_INTERPRETER_BYTECODE_REGISTER_OPTIMIZER_H_
 
 #include "src/base/compiler-specific.h"
 #include "src/globals.h"
 #include "src/interpreter/bytecode-pipeline.h"
@@ skipping 119 matching lines @@
   size_t GetRegisterInfoTableIndex(Register reg) const {
     return static_cast<size_t>(reg.index() + register_info_table_offset_);
   }
 
   Register RegisterFromRegisterInfoTableIndex(size_t index) const {
     return Register(static_cast<int>(index) - register_info_table_offset_);
   }
 
   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_;
   }
 
   Zone* zone() { return zone_; }
 
   const Register accumulator_;
   RegisterInfo* accumulator_info_;
   const Register temporary_base_;
   int max_register_index_;
 
   // Direct mapping to register info.
   ZoneVector<RegisterInfo*> register_info_table_;
   int register_info_table_offset_;
 
   // Counter for equivalence sets identifiers.
   int equivalence_id_;
 
   BytecodePipelineStage* next_stage_;
   bool flush_required_;
   Zone* zone_;
 
   DISALLOW_COPY_AND_ASSIGN(BytecodeRegisterOptimizer);
 };
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_INTERPRETER_BYTECODE_REGISTER_OPTIMIZER_H_