Code reshuffle.
* frame.h (struct frame_arg): New definition.
(read_frame_arg): New declaration.
* mi/mi-cmd-stack.c (list_arg_or_local): New functiom from ...
(list_args_or_locals): ... the code here. New variable arg, call
read_frame_arg and list_arg_or_local with it. Unify the
PRINT_SIMPLE_VALUES and PRINT_ALL_VALUES cases. Call xfree for
arg.error.
* stack.c (print_frame_arg): New functiom from the code of
print_frame_args.
(read_frame_arg): New function.
(print_frame_args): Remove variable val. New variable arg, call
read_frame_arg and print_frame_arg with it. Call xfree for arg.error.