fix bug with @#ifdef in macroprocessor

(cherry picked from commit ebc7a783)

preprocessor/macro/MacroDriver.cc

@@ -170,15 +170,11 @@ MacroDriver::begin_ifdef(const string &name)
   try
     {
       get_variable(name);
-      const MacroValue *one = new IntMV(*this, 1);
-      begin_if(one);
-      delete one;
+      begin_if(new IntMV(*this, 1));
     }
   catch (UnknownVariable &)
     {
-      const MacroValue *zero = new IntMV(*this, 0);
-      begin_if(zero);
-      delete zero;
+      begin_if(new IntMV(*this, 0));
     }
 }