[gn] Enable stricter build flags

src/heap/spaces.h

 // Copyright 2011 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_HEAP_SPACES_H_
 #define V8_HEAP_SPACES_H_
 
 #include <list>
 #include <memory>
 #include <unordered_set>
@@ skipping 516 matching lines @@
   inline Address MarkbitIndexToAddress(uint32_t index) const {
     return this->address() + (index << kPointerSizeLog2);
   }
 
   void ClearLiveness();
 
   void PrintMarkbits() { markbits()->Print(); }
 
   void SetFlag(Flag flag) { flags_ |= flag; }
   void ClearFlag(Flag flag) { flags_ &= ~Flags(flag); }
-  bool IsFlagSet(Flag flag) { return flags_ & flag; }
+  bool IsFlagSet(Flag flag) { return (flags_ & flag) != 0; }
 
   // Set or clear multiple flags at a time. The flags in the mask are set to
   // the value in "flags", the rest retain the current value in |flags_|.
   void SetFlags(uintptr_t flags, uintptr_t mask) {
     flags_ = (flags_ & ~Flags(mask)) | (Flags(flags) & Flags(mask));
   }
 
   // Return all current flags.
   uintptr_t GetFlags() { return flags_; }
 
@@ skipping 2409 matching lines @@
   PageIterator old_iterator_;
   PageIterator code_iterator_;
   PageIterator map_iterator_;
   LargePageIterator lo_iterator_;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_SPACES_H_