[gn] Enable stricter build flags

src/objects.h

 // Copyright 2015 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_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include <iosfwd>
 #include <memory>
 
@@ skipping 10113 matching lines @@
   // Layout description.
   static const int kToNumberRawOffset = HeapObject::kHeaderSize;
   static const int kToStringOffset = kToNumberRawOffset + kDoubleSize;
   static const int kToNumberOffset = kToStringOffset + kPointerSize;
   static const int kTypeOfOffset = kToNumberOffset + kPointerSize;
   static const int kKindOffset = kTypeOfOffset + kPointerSize;
   static const int kSize = kKindOffset + kPointerSize;
 
   static const byte kFalse = 0;
   static const byte kTrue = 1;
-  static const byte kNotBooleanMask = ~1;
+  static const byte kNotBooleanMask = static_cast<byte>(~1);
   static const byte kTheHole = 2;
   static const byte kNull = 3;
   static const byte kArgumentsMarker = 4;
   static const byte kUndefined = 5;
   static const byte kUninitialized = 6;
   static const byte kOther = 7;
   static const byte kException = 8;
   static const byte kOptimizedOut = 9;
   static const byte kStaleRegister = 10;
 
@@ skipping 1430 matching lines @@
   }
 };
 
 
 }  // NOLINT, false-positive due to second-order macros.
 }  // NOLINT, false-positive due to second-order macros.
 
 #include "src/objects/object-macros-undef.h"
 
 #endif  // V8_OBJECTS_H_