output_section_callback, gc_section_callback): New functions for
     generic section walks.
     (wild, lang_gc_wild): Use walk_wild.
     (wild_file, lang_gc_wild_file): Deleted. Common logic moved to
     walk_wild_file.
     (wild_section, lang_gc_wild_section): Deleted. Common logic moved
     to walk_fild_section.  Unique logic moved into callbacks
     output_section_callback and gc_section_callback.