Introduce unop_ind_operation

Introduce unop_ind_operation

This adds class unop_ind_operation, which implements UNOP_IND.

gdb/ChangeLog
2021-03-08  Tom Tromey  <tom@tromey.com>

	* expop.h (class unop_ind_base_operation)
	(class unop_ind_operation): New.
	* eval.c (eval_op_ind): No longer static.  Remove "op" parameter.
	(unop_ind_base_operation::evaluate_for_address)
	(unop_ind_base_operation::evaluate_for_sizeof): New method.
	* ax-gdb.c (gen_expr_unop) <case UNOP_IND>: New.