vla: enable sizeof operator for indirection

vla: enable sizeof operator for indirection

This patch enables the sizeof operator for indirections:

1| void foo (size_t n) {
2|   int vla[n];
3|   int *vla_ptr = &vla;
4| }

(gdb) p sizeof(*vla_ptr)

yields sizeof (size_t) * n.

gdb/ChangeLog:

	* eval.c (evaluate_subexp_for_sizeof) <UNOP_IND>: Create an indirect
	value and retrieve the dynamic type size.