[analyzer] Correctly devirtualize virtual method calls in destructors.

C++11 [class.cdtor]p4: When a virtual function is called directly or
  indirectly from a constructor or from a destructor, including during
  the construction or destruction of the class’s non-static data members,
  and the object to which the call applies is the object under
  construction or destruction, the function called is the final overrider
  in the constructor's or destructor's class and not one overriding it in
  a more-derived class.

llvm-svn: 161915