Merge branch 'jk/unused-post-2.40-part2'

Code clean-up for "-Wunused-parameter" build. * jk/unused-post-2.40-part2: parse-options: drop parse_opt_unknown_cb() t/helper: mark unused argv/argc arguments mark "argv" as unused when we check argc builtins: mark unused prefix parameters builtins: annotate always-empty prefix parameters builtins: always pass prefix to parse_options() fast-import: fix file access when run from subdir