Patch: fix unpack-sources to not require GNU find

[Andrew Udvare]

Requesting review.

Patch submitted here a few months ago: https://gerrit.libreoffice.org/c/core/+/107936

The find that comes with macOS is BSD find and does not have -printf.

On macOS: $ man /usr/share/man/man1/find.1 | grep -F printf
(No results)

On Linux: $ man /usr/share/man/man1/find.1* | grep -F printf
       -delete, -exec, -execdir, -ok, -okdir, -fls, -fprint, -fprintf, -ls, -print and -printf.
              -printf with the %F directive to see the types of your filesystems.

Thanks

-- 
Andrew Udvare