PR22187, infinite loop in find_abstract_instance_name

PR22187, infinite loop in find_abstract_instance_name

This patch prevents the simple case of infinite recursion in
find_abstract_instance_name by ensuring that the attributes being
processed are not the same as the previous call.

The patch also does a little cleanup, and leaves in place some changes
to the nested_funcs array that I made when I wrongly thought looping
might occur in scan_unit_for_symbols.

	PR 22187
	* dwarf2.c (find_abstract_instance_name): Add orig_info_ptr and
	pname param.  Return status.  Make name const.  Don't abort,
	return an error.  Formatting.  Exit if current info_ptr matches
	orig_info_ptr.  Update callers.
	(scan_unit_for_symbols): Start at nesting_level of zero.  Make
	nested_funcs an array of structs for extensibility.  Formatting.