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.