[ Reason ]
Fix FTBFS Bug #1136759.

Debian 13.7 had a glibc update to support the trixie-backport
kernel which made some packages (just a few) not to build anymore.
This is one of them.

[ Impact ]
Anybody trying to build the package under current trixie will find
that the package unexpectedly does not build.

[ Tests ]
I've checked that the package builds ok again.

[ Risks ]
Extremely low.

[ Checklist ]
   [X] *all* changes are documented in the d/changelog
   [X] I reviewed all changes and I approve them
   [X] attach debdiff against the package in (old)stable
   [X] the issue is verified as fixed in unstable

[ Changes ]
See changelog. We are merely adding #include <fcntl.h> to be
able to use the open() function.

[ Other info ]
Change is trivial, so I'm uploading the package next to filing this bug.