[Bug other/91084] download_prerequisites fails on OpenBSD

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91084

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Or you could always just download the packages and untar them by hand. The
script isn't mandatory, it's just a convenience.