[build2] Build error on openbsd 7.1

[Boris Kolpackov]

Dirty Dawn via users <users at build2.org> writes:

> ok, I received the answer, it is written on the pax command page in
> the -x flag where it says that the default format is ustar.
> I did a little test, [...]

Great, thanks for the confirmation.

Did you hear anything about how to achieve -O|--to-stdout when
extracting (-x) a specific file?

So far, the only alternative seems to be to tell the users to
install either GNU tar or BSD tar and use that with bpkg. But
I wonder if there is a way to achieve the same with the base
tools. I skimmed through the pax man page but couldn't see
anything promising.