Fix -Werror=sign-compare error with GCC

src/frames.cc

 // Copyright 2012 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.
 
 #include "src/frames.h"
 
 #include <sstream>
 
 #include "src/v8.h"
 
@@ skipping 942 matching lines @@
         receiver = isolate()->heap()->undefined_value();
       }
 
       Code* const code = shared_info->code();
       DeoptimizationOutputData* const output_data =
           DeoptimizationOutputData::cast(code->deoptimization_data());
       unsigned const entry =
           Deoptimizer::GetOutputInfo(output_data, ast_id, shared_info);
       unsigned const pc_offset =
           FullCodeGenerator::PcField::decode(entry) + Code::kHeaderSize;
-      DCHECK_NE(0, pc_offset);
+      DCHECK_NE(0U, pc_offset);
 
       FrameSummary summary(receiver, function, code, pc_offset, is_constructor);
       frames->Add(summary);
       is_constructor = false;
     } else if (opcode == Translation::CONSTRUCT_STUB_FRAME) {
       // The next encountered JS_FRAME will be marked as a constructor call.
       it.Skip(Translation::NumberOfOperandsFor(opcode));
       DCHECK(!is_constructor);
       is_constructor = true;
     } else {
@@ skipping 562 matching lines @@
   for (StackFrameIterator it(isolate); !it.done(); it.Advance()) {
     StackFrame* frame = AllocateFrameCopy(it.frame(), zone);
     list.Add(frame, zone);
   }
   return list.ToVector();
 }
 
 
 }  // namespace internal
 }  // namespace v8