Your package contains code that is licensed under Sun RPC which is not
documented in the copyright file. Most of the included code's upstream
was relicensed in glibc and Free BSD under BSD-3-Clause.

You can make the package build without the code in question by using the
attached patch (which has two replacement implementations for xdr_seek
and xdr_tell) and adding libtirpc-dev to the Build-Depends.

It would obviously be better to repack the source to get rid of the
code in the source package as well.