Your package fails to build with the newest autoconf-2.71, which was part of a recent wide Fedora change. More information about Fedora autoconf Change available here: https://fedoraproject.org/wiki/Changes/Autoconf_271#How_To_Test. The easiest way to reproduce the problem is to execute a fedora scratch-build on your package. Thank you for cooperation!
What is the actual problem? I've just compiled nbdkit with autoconf 2.71 on my local machine and it works fine.
This was an automated created tracker, if the package builds, please close it. Thank you.
https://koji.fedoraproject.org/koji/buildinfo?buildID=1826107