I see that there is a new upstream version available (debian/watch is out of date, the current site seems to be https://www.uni-due.de/~be0001/rserpool/), and it does fix this build failure. Attached is a debdiff against the packaging for this, but it's incomplete because librsplib2 has an ABI-breaking change without an soname change, so that would need to be resolved. In any case, I'm not planning to upload this to the archive as-is; someone would need to show interest in keeping this package in Ubuntu long-term for me to be willing to do so.
I see that there is a new upstream version available (debian/watch is out of date, the current site seems to be https:/ /www.uni- due.de/ ~be0001/ rserpool/), and it does fix this build failure. Attached is a debdiff against the packaging for this, but it's incomplete because librsplib2 has an ABI-breaking change without an soname change, so that would need to be resolved. In any case, I'm not planning to upload this to the archive as-is; someone would need to show interest in keeping this package in Ubuntu long-term for me to be willing to do so.