For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:Sauerland:Graphics/openSUSE_Tumbleweed/home:Sauerland:Graphics.repo
zypper refresh
zypper install autoconf
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:Sauerland:Graphics/15.6/home:Sauerland:Graphics.repo
zypper refresh
zypper install autoconf
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:Sauerland:Graphics/15.5/home:Sauerland:Graphics.repo
zypper refresh
zypper install autoconf