vec.h: add auto_delete_vec

vec.h: add auto_delete_vec

This patch adds a class auto_delete_vec<T>, a subclass of auto_vec <T *>
that deletes all of its elements on destruction; it's used in many
places in the analyzer patch kit.

This is a crude way for a vec to "own" the objects it points to
and clean up automatically (essentially a workaround for not being able
to use unique_ptr, due to C++98).

gcc/ChangeLog:
	* vec.c (class selftest::count_dtor): New class.
	(selftest::test_auto_delete_vec): New test.
	(selftest::vec_c_tests): Call it.
	* vec.h (class auto_delete_vec): New class template.
	(auto_delete_vec<T>::~auto_delete_vec): New dtor.

From-SVN: r280027