Here's a snippet from my machine changelogs. I needed libxml in slink, but it isn't a package, so I retrieved the sources from unstable and built them. At the end I discovered:
I had to create a symbolic link by hand in /usr/include ln -s libxml2/libxml libxml (e.g. /usr/include/libxml points to /usr/include/libxml2/libxml) I think this directory structure is a bug in the package.