Commit fcfba37337 ('ref-filter: make "--contains <id>" less chatty if
<id> is invalid', 2018-02-23) added the add_str_to_commit_list()
function, which causes sparse to issue a "... not declared. Should it
be static?" warning for that symbol.
Indeed, the function is only used in this one compilation unit. Mark
it static.
Signed-off-by: Ramsay Jones <ramsay@ramsayjones.plus.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>