beos.em qsort predicate tidy

beos.em qsort predicate tidy

lang_input_section_type** is better than lang_statement_union_type**
here since that is in fact the type passed to the qsort predicate,
and I think it's worth factoring out the common indirections.

	* emultempl/beos.em (sort_by_file_name): Use appropriate
	intermediary variables.
	(sort_by_section_name): Likewise.