https://fedoraproject.org/wiki/Changes/Autoconf_271#How_To_Test

As I think this is not trivial we should add to How_To_Test paragraph :

After:
copr mock-config odubaj/autoconf-2.70 fedora-rawhide-x86_64  > odubaj-autoconf-2.70_fedora-34-x86_64.cfg
mv odubaj-autoconf-2.70_fedora-34-x86_64.cfg /etc/mock

we may run:
mock -r odubaj-autoconf-2.70_fedora-rawhide-x86_64 --rebuild ufraw-0.23-0.11.20210413.fc35.src.rpm

Than you
--
Sérgio M. B.