We will need the command invocation path in system_path(). This path was
passed to setup_path(), but system_path() can be called earlier, for
example via:
main
commit_pager_choice
setup_pager
git_config
git_etc_gitconfig
system_path
Therefore, we introduce git_set_argv0_path() and call it as soon as
possible.
Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at> Signed-off-by: Junio C Hamano <gitster@pobox.com>