dmd2/src/druntime/import/core/sys/posix/sys/un.di is missing in dmd.2.057.zip downloaded form here: (https://github.com/downloads/D-Programming-Language/dmd/dmd.2.057.zip). But it's corresponding *.d file seems to be present dmd2/src/druntime/src/core/sys/posix/sys/un.d. The problem occurs when Jordi uses the zip file as a base for *.deb packages and ONLY includes the *.di files.
This version is so old already that I think marking this as WONTFIX is appropriate here.