fix up xml-support.c

fix up xml-support.c

xml-support.c has a function that returns a cleanup via an out parameter.

This changes this function to be a normal cleanup constructor --
returning the cleanup directly and returning the other result via an
out parameter.

This is sort of a hack, but it lets the checker work here.

I also noticed that gdb_xml_create_parser_and_cleanup does not need to
be exported any more.

	* xml-support.c (gdb_xml_create_parser_and_cleanup): Rename from
	gdb_xml_create_parser_and_cleanup_1.  Return a cleanup.  Remove
	'old_chain' argument.  Add 'parser_result' argument.
	(gdb_xml_create_parser_and_cleanup): Remove old version.
	(gdb_xml_parse_quick): Update.
	(xml_process_xincludes): Update.
	* xml-support.h (gdb_xml_create_parser_and_cleanup): Don't
	declare.