Fix GCC 4.7 warnings:

src/debug.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1128 matching lines @@
 
   PrepareForBreakPoints();
 
   if (!EnsureDebugInfo(shared)) {
     // Return if retrieving debug info failed.
     return;
   }
 
   Handle<DebugInfo> debug_info = GetDebugInfo(shared);
   // Source positions starts with zero.
-  ASSERT(source_position >= 0);
+  ASSERT(*source_position >= 0);
 
   // Find the break point and change it.
   BreakLocationIterator it(debug_info, SOURCE_BREAK_LOCATIONS);
   it.FindBreakLocationFromPosition(*source_position);
   it.SetBreakPoint(break_point_object);
 
   *source_position = it.position();
 
   // At least one active break point now.
   ASSERT(debug_info->GetBreakPointCount() > 0);
@@ skipping 2330 matching lines @@
     {
       Locker locker;
       Isolate::Current()->debugger()->CallMessageDispatchHandler();
     }
   }
 }
 
 #endif  // ENABLE_DEBUGGER_SUPPORT
 
 } }  // namespace v8::internal