Comment 2 for bug 2039234

The issue isn't because of libc6-dev:i386, which is a multiarch package and should cope just fine with sharing an identical file with its :amd64 counterpart. The issue is in the biarch package libc6-dev-i386:amd64.

What happened is that the fortran header was moved into an arch-specific directory in the -dev packages for the 2.38, and instead the biarch packages inserted a symlink in the generic path. That particular change was picked up when I merged the Debian changes, but I didn't notice the symlink part. What this means is that the 2.38 biarch packages need to declare a Breaks+Replace relationship on the -dev packages << 2.37.

This will be fixed in an upcoming SRU. Meanwhile, to be able to upgrade the easiest thing that comes to mind is to remove the biarch package before upgrade and reinstall afterwards. Sorry for the inconvenience!